Search criteria
4 vulnerabilities found for workers-oauth-provider by cloudflare
CVE-2025-4144 (GCVE-0-2025-4144)
Vulnerability from nvd – Published: 2025-05-01 00:50 – Updated: 2025-05-01 15:33
VLAI?
Title
PKCE bypass via downgrade attack
Summary
PKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp . However, it was found that an attacker could cause the check to be skipped.
Fixed in:
https://github.com/cloudflare/workers-oauth-provider/pull/27 https://github.com/cloudflare/workers-oauth-provider/pull/27
Impact:
PKCE is a defense-in-depth mechanism against certain kinds of attacks and was an optional extension in OAuth 2.0 which became required in the OAuth 2.1 draft. (Note that the MCP specification requires OAuth 2.1.). This bug completely bypasses PKCE protection.
Severity ?
CWE
- CWE-287 - Improper Authentication
Assigner
References
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2025-4144",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2025-05-01T14:30:41.553527Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2025-05-01T15:33:23.092Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://github.com/cloudflare",
"defaultStatus": "unaffected",
"packageName": "workers-oauth-provider",
"repo": "https://github.com/cloudflare/workers-oauth-provider",
"versions": [
{
"lessThan": "0.0.5",
"status": "affected",
"version": "0",
"versionType": "git"
}
]
}
],
"datePublic": "2025-04-30T16:30:00.000Z",
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003ePKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of \u003c/span\u003e\u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/workers-mcp\"\u003e\u003cspan style=\"background-color: transparent;\"\u003eMCP framework\u003c/span\u003e\u003c/a\u003e. However, it\u003cspan style=\"background-color: transparent;\"\u003e\u0026nbsp;was found that an attacker could cause the check to be skipped.\u003c/span\u003e\u003c/p\u003e\u003cb\u003e\u003cbr\u003e\u003c/b\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eFixed in:\u003c/span\u003e\u003c/p\u003e\u003cp\u003e \u003c/p\u003e\u003cp\u003e\u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/workers-oauth-provider/pull/27\"\u003e\u003cspan style=\"background-color: transparent;\"\u003ehttps://github.com/cloudflare/workers-oauth-provider/pull/27\u003c/span\u003e\u003c/a\u003e\u003c/p\u003e\u003cb\u003e\u003cbr\u003e\u003c/b\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eImpact: \u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003ePKCE is a defense-in-depth mechanism against certain kinds of attacks and was an optional extension in OAuth 2.0 which became required in the OAuth 2.1 draft. (Note that the MCP specification requires OAuth 2.1.).\u0026nbsp;\u003c/span\u003e\u003cspan style=\"background-color: transparent;\"\u003eThis bug completely bypasses PKCE protection.\u003c/span\u003e\u003c/p\u003e\u003cbr\u003e"
}
],
"value": "PKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp . However, it\u00a0was found that an attacker could cause the check to be skipped.\n\n\nFixed in:\n\n \n\n https://github.com/cloudflare/workers-oauth-provider/pull/27 https://github.com/cloudflare/workers-oauth-provider/pull/27 \n\n\nImpact: \n\nPKCE is a defense-in-depth mechanism against certain kinds of attacks and was an optional extension in OAuth 2.0 which became required in the OAuth 2.1 draft. (Note that the MCP specification requires OAuth 2.1.).\u00a0This bug completely bypasses PKCE protection."
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 5.3,
"baseSeverity": "MEDIUM",
"privilegesRequired": "NONE",
"providerUrgency": "AMBER",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "PASSIVE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/U:Amber",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "LOW",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-287",
"description": "CWE-287 Improper Authentication",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2025-05-01T00:50:27.543Z",
"orgId": "a22f1246-ba21-4bb4-a601-ad51614c1513",
"shortName": "cloudflare"
},
"references": [
{
"url": "https://github.com/cloudflare/workers-oauth-provider/pull/27"
}
],
"source": {
"discovery": "UNKNOWN"
},
"title": "PKCE bypass via downgrade attack",
"x_generator": {
"engine": "Vulnogram 0.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "a22f1246-ba21-4bb4-a601-ad51614c1513",
"assignerShortName": "cloudflare",
"cveId": "CVE-2025-4144",
"datePublished": "2025-05-01T00:50:27.543Z",
"dateReserved": "2025-04-30T16:39:00.801Z",
"dateUpdated": "2025-05-01T15:33:23.092Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.1"
}
CVE-2025-4143 (GCVE-0-2025-4143)
Vulnerability from nvd – Published: 2025-05-01 00:19 – Updated: 2025-05-01 15:33
VLAI?
Title
Missing validation of redirect_uri on authorize endpoint
Summary
The OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp , did not correctly validate that redirect_uri was on the allowed list of redirect URIs for the given client registration.
Fixed in: https://github.com/cloudflare/workers-oauth-provider/pull/26 https://github.com/cloudflare/workers-oauth-provider/pull/26
Impact:
Under certain circumstances (see below), if a victim had previously authorized with a server built on workers-oath-provider, and an attacker could later trick the victim into visiting a malicious web site, then attacker could potentially steal the victim's credentials to the same OAuth server and subsequently impersonate them.
In order for the attack to be possible, the OAuth server's authorized callback must be designed to auto-approve authorizations that appear to come from an OAuth client that the victim has authorized previously. The authorization flow is not implemented by workers-oauth-provider; it is up to the application built on top to decide whether to implement such automatic re-authorization. However, many applications do implement such logic.
Note: It is a basic, well-known requirement that OAuth servers should verify that the redirect URI is among the allowed list for the client, both during the authorization flow and subsequently when exchanging the authorization code for an access token. workers-oauth-provider implemented only the latter check, not the former. Unfortunately, the former is the much more important check. Readers who are familiar with OAuth may recognize that failing to check redirect URIs against the allowed list is a well-known, basic mistake, covered extensively in the RFC and elsewhere. The author of this library would like everyone to know that he was, in fact, well-aware of this requirement, thought about it a lot while designing the library, and then, somehow, forgot to actually make sure the check was in the code. That is, it's not that he didn't know what he was doing, it's that he knew what he was doing but flubbed it.
Severity ?
CWE
- CWE-601 - URL Redirection to Untrusted Site ('Open Redirect')
Assigner
References
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2025-4143",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2025-05-01T14:34:12.301406Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2025-05-01T15:33:28.911Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://github.com/cloudflare",
"defaultStatus": "unaffected",
"packageName": "workers-oauth-provider",
"repo": "https://github.com/cloudflare/workers-oauth-provider",
"versions": [
{
"lessThan": "0.0.5",
"status": "affected",
"version": "0",
"versionType": "git"
}
]
}
],
"datePublic": "2025-04-30T16:30:00.000Z",
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eThe OAuth implementation in workers-oauth-provider that is part of \u003c/span\u003e\u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/workers-mcp\"\u003e\u003cspan style=\"background-color: transparent;\"\u003eMCP framework\u003c/span\u003e\u003c/a\u003e\u003cspan style=\"background-color: transparent;\"\u003e, did not correctly validate that redirect_uri was on the allowed list of redirect URIs for the given client registration.\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003e\u003cb\u003eFixed in:\u0026nbsp;\u003c/b\u003e\u003c/span\u003e\u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/workers-oauth-provider/pull/26\"\u003e\u003cspan style=\"background-color: transparent;\"\u003ehttps://github.com/cloudflare/workers-oauth-provider/pull/26\u003c/span\u003e\u003c/a\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003e\u003cb\u003eImpact:\u003c/b\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e \u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eUnder certain circumstances (see below), if a victim had previously authorized with a server built on workers-oath-provider, and an attacker could later trick the victim into visiting a malicious web site, then attacker could potentially steal the victim\u0027s credentials to the same OAuth server and subsequently impersonate them.\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eIn order for the attack to be possible, the OAuth server\u0027s authorized callback must be designed to auto-approve authorizations that appear to come from an OAuth client that the victim has authorized previously. The authorization flow is not implemented by workers-oauth-provider; it is up to the application built on top to decide whether to implement such automatic re-authorization. However, many applications do implement such logic.\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003e\u003ci\u003eNote: It is a basic, well-known requirement that OAuth servers should verify that the redirect URI is among the allowed list for the client, both during the authorization flow and subsequently when exchanging the authorization code for an access token. workers-oauth-provider implemented only the latter check, not the former. Unfortunately, the former is the much more important check.\u0026nbsp;\u003c/i\u003e\u003c/span\u003e\u003cspan style=\"background-color: transparent;\"\u003e\u003ci\u003eReaders who are familiar with OAuth may recognize that failing to check redirect URIs against the allowed list is a well-known, basic mistake, covered extensively in the RFC and elsewhere. The author of this library would like everyone to know that he was, in fact, well-aware of this requirement, thought about it a lot while designing the library, and then, somehow, forgot to actually make sure the check was in the code. That is, it\u0027s not that he didn\u0027t know what he was doing, it\u0027s that he knew what he was doing but flubbed it.\u003c/i\u003e\u003c/span\u003e\u003c/p\u003e"
}
],
"value": "The OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp , did not correctly validate that redirect_uri was on the allowed list of redirect URIs for the given client registration.\n\nFixed in:\u00a0 https://github.com/cloudflare/workers-oauth-provider/pull/26 https://github.com/cloudflare/workers-oauth-provider/pull/26 \n\nImpact:\n\n \n\nUnder certain circumstances (see below), if a victim had previously authorized with a server built on workers-oath-provider, and an attacker could later trick the victim into visiting a malicious web site, then attacker could potentially steal the victim\u0027s credentials to the same OAuth server and subsequently impersonate them.\n\nIn order for the attack to be possible, the OAuth server\u0027s authorized callback must be designed to auto-approve authorizations that appear to come from an OAuth client that the victim has authorized previously. The authorization flow is not implemented by workers-oauth-provider; it is up to the application built on top to decide whether to implement such automatic re-authorization. However, many applications do implement such logic.\n\nNote: It is a basic, well-known requirement that OAuth servers should verify that the redirect URI is among the allowed list for the client, both during the authorization flow and subsequently when exchanging the authorization code for an access token. workers-oauth-provider implemented only the latter check, not the former. Unfortunately, the former is the much more important check.\u00a0Readers who are familiar with OAuth may recognize that failing to check redirect URIs against the allowed list is a well-known, basic mistake, covered extensively in the RFC and elsewhere. The author of this library would like everyone to know that he was, in fact, well-aware of this requirement, thought about it a lot while designing the library, and then, somehow, forgot to actually make sure the check was in the code. That is, it\u0027s not that he didn\u0027t know what he was doing, it\u0027s that he knew what he was doing but flubbed it."
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "HIGH",
"attackRequirements": "PRESENT",
"attackVector": "NETWORK",
"baseScore": 6,
"baseSeverity": "MEDIUM",
"privilegesRequired": "NONE",
"providerUrgency": "AMBER",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "LOW",
"subIntegrityImpact": "NONE",
"userInteraction": "PASSIVE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:N/VA:N/SC:L/SI:N/SA:N/U:Amber",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "NONE",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-601",
"description": "CWE-601 URL Redirection to Untrusted Site (\u0027Open Redirect\u0027)",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2025-05-01T00:19:52.737Z",
"orgId": "a22f1246-ba21-4bb4-a601-ad51614c1513",
"shortName": "cloudflare"
},
"references": [
{
"url": "https://github.com/cloudflare/workers-oauth-provider/pull/26"
}
],
"source": {
"discovery": "UNKNOWN"
},
"title": "Missing validation of redirect_uri on authorize endpoint",
"x_generator": {
"engine": "Vulnogram 0.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "a22f1246-ba21-4bb4-a601-ad51614c1513",
"assignerShortName": "cloudflare",
"cveId": "CVE-2025-4143",
"datePublished": "2025-05-01T00:19:52.737Z",
"dateReserved": "2025-04-30T16:36:33.506Z",
"dateUpdated": "2025-05-01T15:33:28.911Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.1"
}
CVE-2025-4144 (GCVE-0-2025-4144)
Vulnerability from cvelistv5 – Published: 2025-05-01 00:50 – Updated: 2025-05-01 15:33
VLAI?
Title
PKCE bypass via downgrade attack
Summary
PKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp . However, it was found that an attacker could cause the check to be skipped.
Fixed in:
https://github.com/cloudflare/workers-oauth-provider/pull/27 https://github.com/cloudflare/workers-oauth-provider/pull/27
Impact:
PKCE is a defense-in-depth mechanism against certain kinds of attacks and was an optional extension in OAuth 2.0 which became required in the OAuth 2.1 draft. (Note that the MCP specification requires OAuth 2.1.). This bug completely bypasses PKCE protection.
Severity ?
CWE
- CWE-287 - Improper Authentication
Assigner
References
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2025-4144",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2025-05-01T14:30:41.553527Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2025-05-01T15:33:23.092Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://github.com/cloudflare",
"defaultStatus": "unaffected",
"packageName": "workers-oauth-provider",
"repo": "https://github.com/cloudflare/workers-oauth-provider",
"versions": [
{
"lessThan": "0.0.5",
"status": "affected",
"version": "0",
"versionType": "git"
}
]
}
],
"datePublic": "2025-04-30T16:30:00.000Z",
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003ePKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of \u003c/span\u003e\u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/workers-mcp\"\u003e\u003cspan style=\"background-color: transparent;\"\u003eMCP framework\u003c/span\u003e\u003c/a\u003e. However, it\u003cspan style=\"background-color: transparent;\"\u003e\u0026nbsp;was found that an attacker could cause the check to be skipped.\u003c/span\u003e\u003c/p\u003e\u003cb\u003e\u003cbr\u003e\u003c/b\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eFixed in:\u003c/span\u003e\u003c/p\u003e\u003cp\u003e \u003c/p\u003e\u003cp\u003e\u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/workers-oauth-provider/pull/27\"\u003e\u003cspan style=\"background-color: transparent;\"\u003ehttps://github.com/cloudflare/workers-oauth-provider/pull/27\u003c/span\u003e\u003c/a\u003e\u003c/p\u003e\u003cb\u003e\u003cbr\u003e\u003c/b\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eImpact: \u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003ePKCE is a defense-in-depth mechanism against certain kinds of attacks and was an optional extension in OAuth 2.0 which became required in the OAuth 2.1 draft. (Note that the MCP specification requires OAuth 2.1.).\u0026nbsp;\u003c/span\u003e\u003cspan style=\"background-color: transparent;\"\u003eThis bug completely bypasses PKCE protection.\u003c/span\u003e\u003c/p\u003e\u003cbr\u003e"
}
],
"value": "PKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp . However, it\u00a0was found that an attacker could cause the check to be skipped.\n\n\nFixed in:\n\n \n\n https://github.com/cloudflare/workers-oauth-provider/pull/27 https://github.com/cloudflare/workers-oauth-provider/pull/27 \n\n\nImpact: \n\nPKCE is a defense-in-depth mechanism against certain kinds of attacks and was an optional extension in OAuth 2.0 which became required in the OAuth 2.1 draft. (Note that the MCP specification requires OAuth 2.1.).\u00a0This bug completely bypasses PKCE protection."
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 5.3,
"baseSeverity": "MEDIUM",
"privilegesRequired": "NONE",
"providerUrgency": "AMBER",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "PASSIVE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/U:Amber",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "LOW",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-287",
"description": "CWE-287 Improper Authentication",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2025-05-01T00:50:27.543Z",
"orgId": "a22f1246-ba21-4bb4-a601-ad51614c1513",
"shortName": "cloudflare"
},
"references": [
{
"url": "https://github.com/cloudflare/workers-oauth-provider/pull/27"
}
],
"source": {
"discovery": "UNKNOWN"
},
"title": "PKCE bypass via downgrade attack",
"x_generator": {
"engine": "Vulnogram 0.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "a22f1246-ba21-4bb4-a601-ad51614c1513",
"assignerShortName": "cloudflare",
"cveId": "CVE-2025-4144",
"datePublished": "2025-05-01T00:50:27.543Z",
"dateReserved": "2025-04-30T16:39:00.801Z",
"dateUpdated": "2025-05-01T15:33:23.092Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.1"
}
CVE-2025-4143 (GCVE-0-2025-4143)
Vulnerability from cvelistv5 – Published: 2025-05-01 00:19 – Updated: 2025-05-01 15:33
VLAI?
Title
Missing validation of redirect_uri on authorize endpoint
Summary
The OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp , did not correctly validate that redirect_uri was on the allowed list of redirect URIs for the given client registration.
Fixed in: https://github.com/cloudflare/workers-oauth-provider/pull/26 https://github.com/cloudflare/workers-oauth-provider/pull/26
Impact:
Under certain circumstances (see below), if a victim had previously authorized with a server built on workers-oath-provider, and an attacker could later trick the victim into visiting a malicious web site, then attacker could potentially steal the victim's credentials to the same OAuth server and subsequently impersonate them.
In order for the attack to be possible, the OAuth server's authorized callback must be designed to auto-approve authorizations that appear to come from an OAuth client that the victim has authorized previously. The authorization flow is not implemented by workers-oauth-provider; it is up to the application built on top to decide whether to implement such automatic re-authorization. However, many applications do implement such logic.
Note: It is a basic, well-known requirement that OAuth servers should verify that the redirect URI is among the allowed list for the client, both during the authorization flow and subsequently when exchanging the authorization code for an access token. workers-oauth-provider implemented only the latter check, not the former. Unfortunately, the former is the much more important check. Readers who are familiar with OAuth may recognize that failing to check redirect URIs against the allowed list is a well-known, basic mistake, covered extensively in the RFC and elsewhere. The author of this library would like everyone to know that he was, in fact, well-aware of this requirement, thought about it a lot while designing the library, and then, somehow, forgot to actually make sure the check was in the code. That is, it's not that he didn't know what he was doing, it's that he knew what he was doing but flubbed it.
Severity ?
CWE
- CWE-601 - URL Redirection to Untrusted Site ('Open Redirect')
Assigner
References
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2025-4143",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2025-05-01T14:34:12.301406Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2025-05-01T15:33:28.911Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://github.com/cloudflare",
"defaultStatus": "unaffected",
"packageName": "workers-oauth-provider",
"repo": "https://github.com/cloudflare/workers-oauth-provider",
"versions": [
{
"lessThan": "0.0.5",
"status": "affected",
"version": "0",
"versionType": "git"
}
]
}
],
"datePublic": "2025-04-30T16:30:00.000Z",
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eThe OAuth implementation in workers-oauth-provider that is part of \u003c/span\u003e\u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/workers-mcp\"\u003e\u003cspan style=\"background-color: transparent;\"\u003eMCP framework\u003c/span\u003e\u003c/a\u003e\u003cspan style=\"background-color: transparent;\"\u003e, did not correctly validate that redirect_uri was on the allowed list of redirect URIs for the given client registration.\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003e\u003cb\u003eFixed in:\u0026nbsp;\u003c/b\u003e\u003c/span\u003e\u003ca target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/workers-oauth-provider/pull/26\"\u003e\u003cspan style=\"background-color: transparent;\"\u003ehttps://github.com/cloudflare/workers-oauth-provider/pull/26\u003c/span\u003e\u003c/a\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003e\u003cb\u003eImpact:\u003c/b\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e \u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eUnder certain circumstances (see below), if a victim had previously authorized with a server built on workers-oath-provider, and an attacker could later trick the victim into visiting a malicious web site, then attacker could potentially steal the victim\u0027s credentials to the same OAuth server and subsequently impersonate them.\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003eIn order for the attack to be possible, the OAuth server\u0027s authorized callback must be designed to auto-approve authorizations that appear to come from an OAuth client that the victim has authorized previously. The authorization flow is not implemented by workers-oauth-provider; it is up to the application built on top to decide whether to implement such automatic re-authorization. However, many applications do implement such logic.\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan style=\"background-color: transparent;\"\u003e\u003ci\u003eNote: It is a basic, well-known requirement that OAuth servers should verify that the redirect URI is among the allowed list for the client, both during the authorization flow and subsequently when exchanging the authorization code for an access token. workers-oauth-provider implemented only the latter check, not the former. Unfortunately, the former is the much more important check.\u0026nbsp;\u003c/i\u003e\u003c/span\u003e\u003cspan style=\"background-color: transparent;\"\u003e\u003ci\u003eReaders who are familiar with OAuth may recognize that failing to check redirect URIs against the allowed list is a well-known, basic mistake, covered extensively in the RFC and elsewhere. The author of this library would like everyone to know that he was, in fact, well-aware of this requirement, thought about it a lot while designing the library, and then, somehow, forgot to actually make sure the check was in the code. That is, it\u0027s not that he didn\u0027t know what he was doing, it\u0027s that he knew what he was doing but flubbed it.\u003c/i\u003e\u003c/span\u003e\u003c/p\u003e"
}
],
"value": "The OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp , did not correctly validate that redirect_uri was on the allowed list of redirect URIs for the given client registration.\n\nFixed in:\u00a0 https://github.com/cloudflare/workers-oauth-provider/pull/26 https://github.com/cloudflare/workers-oauth-provider/pull/26 \n\nImpact:\n\n \n\nUnder certain circumstances (see below), if a victim had previously authorized with a server built on workers-oath-provider, and an attacker could later trick the victim into visiting a malicious web site, then attacker could potentially steal the victim\u0027s credentials to the same OAuth server and subsequently impersonate them.\n\nIn order for the attack to be possible, the OAuth server\u0027s authorized callback must be designed to auto-approve authorizations that appear to come from an OAuth client that the victim has authorized previously. The authorization flow is not implemented by workers-oauth-provider; it is up to the application built on top to decide whether to implement such automatic re-authorization. However, many applications do implement such logic.\n\nNote: It is a basic, well-known requirement that OAuth servers should verify that the redirect URI is among the allowed list for the client, both during the authorization flow and subsequently when exchanging the authorization code for an access token. workers-oauth-provider implemented only the latter check, not the former. Unfortunately, the former is the much more important check.\u00a0Readers who are familiar with OAuth may recognize that failing to check redirect URIs against the allowed list is a well-known, basic mistake, covered extensively in the RFC and elsewhere. The author of this library would like everyone to know that he was, in fact, well-aware of this requirement, thought about it a lot while designing the library, and then, somehow, forgot to actually make sure the check was in the code. That is, it\u0027s not that he didn\u0027t know what he was doing, it\u0027s that he knew what he was doing but flubbed it."
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "HIGH",
"attackRequirements": "PRESENT",
"attackVector": "NETWORK",
"baseScore": 6,
"baseSeverity": "MEDIUM",
"privilegesRequired": "NONE",
"providerUrgency": "AMBER",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "LOW",
"subIntegrityImpact": "NONE",
"userInteraction": "PASSIVE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:N/VA:N/SC:L/SI:N/SA:N/U:Amber",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "NONE",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-601",
"description": "CWE-601 URL Redirection to Untrusted Site (\u0027Open Redirect\u0027)",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2025-05-01T00:19:52.737Z",
"orgId": "a22f1246-ba21-4bb4-a601-ad51614c1513",
"shortName": "cloudflare"
},
"references": [
{
"url": "https://github.com/cloudflare/workers-oauth-provider/pull/26"
}
],
"source": {
"discovery": "UNKNOWN"
},
"title": "Missing validation of redirect_uri on authorize endpoint",
"x_generator": {
"engine": "Vulnogram 0.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "a22f1246-ba21-4bb4-a601-ad51614c1513",
"assignerShortName": "cloudflare",
"cveId": "CVE-2025-4143",
"datePublished": "2025-05-01T00:19:52.737Z",
"dateReserved": "2025-04-30T16:36:33.506Z",
"dateUpdated": "2025-05-01T15:33:28.911Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.1"
}