Vulnerability-Lookup

CVE-2026-55766 (GCVE-0-2026-55766)

Vulnerability from cvelistv5 – Published: 2026-06-23 15:07 – Updated: 2026-06-23 15:49

Title

guzzlehttp/psr7: CRLF Injection in HTTP Start-Line Serialization

Summary

guzzlehttp/psr7 is a PSR-7 HTTP message library implementation in PHP. Prior to 2.12.1, guzzlehttp/psr7 did not reject CR/LF characters in certain first-party HTTP start-line fields: the request method, protocol version, and response reason phrase. If an application placed attacker-controlled data into one of those fields and later serialized the PSR-7 message as raw HTTP/1.x, for example with Message::toString() or an equivalent serializer, the serialized message could contain attacker-controlled header lines. The issue can also be reached through Message::parseRequest() or Message::parseResponse() when malformed raw messages are parsed into first-party PSR-7 objects and then serialized again. Creating or modifying a Request, Response, or other PSR-7 object alone is not sufficient. The issue requires the malformed message to be serialized and written to the network, forwarded, replayed, or otherwise processed by software that does not independently reject the malformed start line. This vulnerability is fixed in 2.12.1.

Severity

4.8 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')
CWE-113 - Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/guzzle/psr7/security/advisorie…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
guzzle	psr7	Affected: < 2.12.1

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-55766

Vulnerability from fkie_nvd - Published: 2026-06-23 16:17 - Updated: 2026-06-30 17:17

Severity

4.8 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/guzzle/psr7/security/advisories/GHSA-vm85-hxw5-5432	Mitigation, Vendor Advisory

Impacted products

	Vendor	Product	Version
	guzzlephp	psr-7	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "psr7",
          "vendor": "guzzle",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.12.1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
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              "versionEndExcluding": "2.12.1",
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      "value": "guzzlehttp/psr7 is a PSR-7 HTTP message library implementation in PHP. Prior to 2.12.1, guzzlehttp/psr7 did not reject CR/LF characters in certain first-party HTTP start-line fields: the request method, protocol version, and response reason phrase. If an application placed attacker-controlled data into one of those fields and later serialized the PSR-7 message as raw HTTP/1.x, for example with Message::toString() or an equivalent serializer, the serialized message could contain attacker-controlled header lines. The issue can also be reached through Message::parseRequest() or Message::parseResponse() when malformed raw messages are parsed into first-party PSR-7 objects and then serialized again. Creating or modifying a Request, Response, or other PSR-7 object alone is not sufficient. The issue requires the malformed message to be serialized and written to the network, forwarded, replayed, or otherwise processed by software that does not independently reject the malformed start line. This vulnerability is fixed in 2.12.1."
    }
  ],
  "id": "CVE-2026-55766",
  "lastModified": "2026-06-30T17:17:36.993",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 4.8,
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GHSA-VM85-HXW5-5432

Vulnerability from github – Published: 2026-06-19 14:35 – Updated: 2026-06-19 14:35

Summary

guzzlehttp/psr7: CRLF Injection in HTTP Start-Line Serialization

Details

Impact

guzzlehttp/psr7 did not reject CR/LF characters in certain first-party HTTP start-line fields: the request method, protocol version, and response reason phrase. If an application placed attacker-controlled data into one of those fields and later serialized the PSR-7 message as raw HTTP/1.x, for example with Message::toString() or an equivalent serializer, the serialized message could contain attacker-controlled header lines. The issue can also be reached through Message::parseRequest() or Message::parseResponse() when malformed raw messages are parsed into first-party PSR-7 objects and then serialized again.

Creating or modifying a Request, Response, or other PSR-7 object alone is not sufficient. The issue requires the malformed message to be serialized and written to the network, forwarded, replayed, or otherwise processed by software that does not independently reject the malformed start line. This is not the normal request-sending path used by guzzlehttp/guzzle; applications using guzzlehttp/psr7 only through Guzzle's standard HTTP client APIs are not expected to be affected.

Applications are most likely to be affected when they manually serialize PSR-7 messages, forward raw HTTP messages, or use custom transports, proxying, crawling, webhook delivery, testing, or similar code. Depending on how downstream HTTP/1.1 components parse the serialized message, this may lead to header injection, response splitting, request smuggling, or cache poisoning.

Patches

The issue is patched in 2.12.1 and later. Starting in that release, guzzlehttp/psr7 rejects CR/LF characters in HTTP method, protocol version, and response reason phrase values before storing them in first-party message objects.

Workarounds

If you cannot upgrade immediately, reject CR/LF in untrusted method, protocol version, and reason phrase values before constructing or modifying PSR-7 messages.

Applications that parse, forward, replay, or serialize raw HTTP messages cannot work around the parser entry points by validating only after parsing. They should validate the raw start line before calling Message::parseRequest() or Message::parseResponse(), avoid reparsing untrusted raw messages, or upgrade. If an application runs with attacker-controlled synthetic $_SERVER values, validate REQUEST_METHOD and SERVER_PROTOCOL before calling ServerRequest::fromGlobals().

Severity

4.8 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "guzzlehttp/psr7"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.12.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55766"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113",
      "CWE-93"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T14:35:57Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Impact\n\n`guzzlehttp/psr7` did not reject CR/LF characters in certain first-party HTTP start-line fields: the request method, protocol version, and response reason phrase. If an application placed attacker-controlled data into one of those fields and later serialized the PSR-7 message as raw HTTP/1.x, for example with `Message::toString()` or an equivalent serializer, the serialized message could contain attacker-controlled header lines. The issue can also be reached through `Message::parseRequest()` or `Message::parseResponse()` when malformed raw messages are parsed into first-party PSR-7 objects and then serialized again.\n\nCreating or modifying a `Request`, `Response`, or other PSR-7 object alone is not sufficient. The issue requires the malformed message to be serialized and written to the network, forwarded, replayed, or otherwise processed by software that does not independently reject the malformed start line. This is not the normal request-sending path used by `guzzlehttp/guzzle`; applications using `guzzlehttp/psr7` only through Guzzle\u0027s standard HTTP client APIs are not expected to be affected.\n\nApplications are most likely to be affected when they manually serialize PSR-7 messages, forward raw HTTP messages, or use custom transports, proxying, crawling, webhook delivery, testing, or similar code. Depending on how downstream HTTP/1.1 components parse the serialized message, this may lead to header injection, response splitting, request smuggling, or cache poisoning.\n\n### Patches\n\nThe issue is patched in `2.12.1` and later. Starting in that release, `guzzlehttp/psr7` rejects CR/LF characters in HTTP method, protocol version, and response reason phrase values before storing them in first-party message objects.\n\n### Workarounds\n\nIf you cannot upgrade immediately, reject CR/LF in untrusted method, protocol version, and reason phrase values before constructing or modifying PSR-7 messages.\n\nApplications that parse, forward, replay, or serialize raw HTTP messages cannot work around the parser entry points by validating only after parsing. They should validate the raw start line before calling `Message::parseRequest()` or `Message::parseResponse()`, avoid reparsing untrusted raw messages, or upgrade. If an application runs with attacker-controlled synthetic `$_SERVER` values, validate `REQUEST_METHOD` and `SERVER_PROTOCOL` before calling `ServerRequest::fromGlobals()`.",
  "id": "GHSA-vm85-hxw5-5432",
  "modified": "2026-06-19T14:35:57Z",
  "published": "2026-06-19T14:35:57Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/guzzle/psr7/security/advisories/GHSA-vm85-hxw5-5432"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/guzzle/psr7"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "guzzlehttp/psr7: CRLF Injection in HTTP Start-Line Serialization"
}

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.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-55766 (GCVE-0-2026-55766)

FKIE_CVE-2026-55766

GHSA-VM85-HXW5-5432

Impact

Patches

Workarounds

Tags

Sightings

Nomenclature