FKIE_CVE-2026-66835
Vulnerability from fkie_nvd - Published: 2026-09-01 15:17 - Updated: 2026-09-01 21:15
Severity
Summary
Path Equivalence vulnerability in Erlang/OTP inets httpd allows a remote unauthenticated attacker to read files inside a mod_auth protected directory by prefixing the request path with an extra slash.
httpd_request:validate_uri/1 normalises the request URI with uri_string:normalize/1, which performs RFC 3986 dot-segment removal but does not collapse empty path segments, so a doubled slash survives. mod_alias:real_name/3 concatenates the document root with that URI, and mod_auth:secret_path/3 then decides whether the result lies inside a protected directory block by running the configured directory path as an unanchored regular expression against it. The doubled slash breaks the contiguous substring the regex needs, so the request is treated as unprotected and no authentication challenge is issued, while mod_get opens the same path and the operating system collapses the doubled slash and returns the protected file. The same path mismatch also evades the per-path accounting in mod_security.
This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.
References
Impacted products
| Vendor | Product | Version |
|---|
{
"affected": [
{
"affectedData": [
{
"cpes": [
"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"mod_auth",
"mod_alias",
"httpd_request"
],
"packageName": "otp",
"packageURL": "pkg:sid/erlang.org/otp",
"product": "OTP",
"programFiles": [
"lib/inets/src/http_server/mod_auth.erl",
"lib/inets/src/http_server/mod_alias.erl",
"lib/inets/src/http_server/httpd_request.erl"
],
"programRoutines": [
{
"name": "mod_auth:secret_path/3"
},
{
"name": "mod_alias:real_name/3"
},
{
"name": "httpd_request:validate_uri/1"
}
],
"vendor": "Erlang",
"versions": [
{
"lessThan": "17.0",
"status": "unknown",
"version": "0",
"versionType": "otp"
},
{
"lessThan": "27.3.4.17",
"status": "affected",
"version": "17.0",
"versionType": "otp"
},
{
"lessThan": "28.5.0.6",
"status": "affected",
"version": "28.0",
"versionType": "otp"
},
{
"lessThan": "29.0.6",
"status": "affected",
"version": "29.0",
"versionType": "otp"
}
]
},
{
"cpes": [
"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"mod_auth",
"mod_alias",
"httpd_request"
],
"packageName": "inets",
"packageURL": "pkg:otp/inets",
"product": "OTP",
"programFiles": [
"src/http_server/mod_auth.erl",
"src/http_server/mod_alias.erl",
"src/http_server/httpd_request.erl"
],
"programRoutines": [
{
"name": "mod_auth:secret_path/3"
},
{
"name": "mod_alias:real_name/3"
},
{
"name": "httpd_request:validate_uri/1"
}
],
"repo": "https://github.com/erlang/otp",
"vendor": "Erlang",
"versions": [
{
"lessThan": "5.10",
"status": "unknown",
"version": "0",
"versionType": "otp"
},
{
"lessThan": "9.3.2.7",
"status": "affected",
"version": "5.10",
"versionType": "otp"
},
{
"lessThan": "9.6.2.3",
"status": "affected",
"version": "9.4",
"versionType": "otp"
},
{
"lessThan": "9.7.2",
"status": "affected",
"version": "9.7",
"versionType": "otp"
}
]
},
{
"collectionURL": "https://github.com",
"cpes": [
"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"mod_auth",
"mod_alias",
"httpd_request"
],
"packageName": "erlang/otp",
"packageURL": "pkg:github/erlang/otp",
"product": "OTP",
"programFiles": [
"lib/inets/src/http_server/mod_auth.erl",
"lib/inets/src/http_server/mod_alias.erl",
"lib/inets/src/http_server/httpd_request.erl"
],
"programRoutines": [
{
"name": "mod_auth:secret_path/3"
},
{
"name": "mod_alias:real_name/3"
},
{
"name": "httpd_request:validate_uri/1"
}
],
"repo": "https://github.com/erlang/otp",
"vendor": "Erlang",
"versions": [
{
"changes": [
{
"at": "bac19eb3dbd96cc49b6d8cabc1c04248bf8c79f6",
"status": "unaffected"
},
{
"at": "d8878dec0ececc2eab18e47bb18b472f224ca633",
"status": "unaffected"
},
{
"at": "9641944a2efbf55bea760f8ff7ba777fe3a0961c",
"status": "unaffected"
}
],
"lessThan": "*",
"status": "affected",
"version": "84adefa331c4159d432d22840663c38f155cd4c1",
"versionType": "git"
}
]
}
],
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "Path Equivalence vulnerability in Erlang/OTP inets httpd allows a remote unauthenticated attacker to read files inside a mod_auth protected directory by prefixing the request path with an extra slash.\n\nhttpd_request:validate_uri/1 normalises the request URI with uri_string:normalize/1, which performs RFC 3986 dot-segment removal but does not collapse empty path segments, so a doubled slash survives. mod_alias:real_name/3 concatenates the document root with that URI, and mod_auth:secret_path/3 then decides whether the result lies inside a protected directory block by running the configured directory path as an unanchored regular expression against it. The doubled slash breaks the contiguous substring the regex needs, so the request is treated as unprotected and no authentication challenge is issued, while mod_get opens the same path and the operating system collapses the doubled slash and returns the protected file. The same path mismatch also evades the per-path accounting in mod_security.\n\nThis issue affects OTP from OTP\u00a017.0 before OTP\u00a027.3.4.17, from OTP\u00a028.0 before OTP\u00a028.5.0.6, and from OTP\u00a029.0 before OTP\u00a029.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP\u00a017.0, corresponding to inets before 5.10, is affected is unknown."
}
],
"id": "CVE-2026-66835",
"lastModified": "2026-09-01T21:15:00.147",
"metrics": {
"cvssMetricV40": [
{
"cvssData": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "PRESENT",
"attackVector": "NETWORK",
"availabilityRequirement": "NOT_DEFINED",
"baseScore": 8.2,
"baseSeverity": "HIGH",
"confidentialityRequirement": "NOT_DEFINED",
"exploitMaturity": "NOT_DEFINED",
"integrityRequirement": "NOT_DEFINED",
"modifiedAttackComplexity": "NOT_DEFINED",
"modifiedAttackRequirements": "NOT_DEFINED",
"modifiedAttackVector": "NOT_DEFINED",
"modifiedPrivilegesRequired": "NOT_DEFINED",
"modifiedSubAvailabilityImpact": "NOT_DEFINED",
"modifiedSubConfidentialityImpact": "NOT_DEFINED",
"modifiedSubIntegrityImpact": "NOT_DEFINED",
"modifiedUserInteraction": "NOT_DEFINED",
"modifiedVulnAvailabilityImpact": "NOT_DEFINED",
"modifiedVulnConfidentialityImpact": "NOT_DEFINED",
"modifiedVulnIntegrityImpact": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "NONE",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2026-66835",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-09-01T17:57:48.578657Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-09-01T15:17:23.433",
"references": [
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://cna.erlef.org/cves/CVE-2026-66835.html"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/erlang/otp/commit/9641944a2efbf55bea760f8ff7ba777fe3a0961c"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/erlang/otp/commit/bac19eb3dbd96cc49b6d8cabc1c04248bf8c79f6"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/erlang/otp/commit/d8878dec0ececc2eab18e47bb18b472f224ca633"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/erlang/otp/security/advisories/GHSA-r4vv-vc2c-2fw6"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-66835"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://www.erlang.org/doc/system/versions.html#order-of-versions"
}
],
"sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"vulnStatus": "Deferred",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-50"
}
],
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
}
]
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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