Vulnerability-Lookup

GHSA-G2WM-735Q-3F56

Vulnerability from github – Published: 2026-05-11 21:31 – Updated: 2026-05-18 17:48

Summary

cowlib: Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1

Details

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields.

cow_cookie:cookie/1 in cowlib builds a client-side Cookie: request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject ;, ,, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting "; admin=1" to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (parse_cookie_name/1, parse_cookie_value/1) and setcookie/3 already validate and reject these characters; the encoder alone is missing the check.

This issue affects cowlib from 2.9.0.

Severity

2.1 (Low)


                  
                    CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Hex",
        "name": "cowlib"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.9.0"
            },
            {
              "last_affected": "2.16.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-43969"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-93"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-18T17:48:35Z",
    "nvd_published_at": "2026-05-11T19:16:25Z",
    "severity": "LOW"
  },
  "details": "Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027) vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields.\n\ncow_cookie:cookie/1 in cowlib builds a client-side Cookie: request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject ;, ,, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting \"; admin=1\" to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (parse_cookie_name/1, parse_cookie_value/1) and setcookie/3 already validate and reject these characters; the encoder alone is missing the check.\n\nThis issue affects cowlib from 2.9.0.",
  "id": "GHSA-g2wm-735q-3f56",
  "modified": "2026-05-18T17:48:35Z",
  "published": "2026-05-11T21:31:34Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-43969"
    },
    {
      "type": "WEB",
      "url": "https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-43969.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ninenines/cowlib"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-43969"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "cowlib: Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1"
}

CVE-2026-43969 (GCVE-0-2026-43969)

Vulnerability from cvelistv5 – Published: 2026-05-11 18:06 – Updated: 2026-05-12 04:26

Title

Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1

Summary

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields. cow_cookie:cookie/1 in cowlib builds a client-side Cookie: request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject ;, ,, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting "; admin=1" to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (parse_cookie_name/1, parse_cookie_value/1) and setcookie/3 already validate and reject these characters; the encoder alone is missing the check. This issue affects cowlib from 2.9.0.

Severity

2.1 (Low)


                        
                          CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

CWE

CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')

Assigner

EEF

References

3 references

URL	Tags
https://cna.erlef.org/cves/CVE-2026-43969.html	relatedthird-party-advisory
https://osv.dev/vulnerability/EEF-CVE-2026-43969	related
https://github.com/erlef/cowlib/commit/177953dd51…	patch

Impacted products

2 products

Vendor	Product	Version
ninenines	cowlib	Affected: 2.9.0 (semver) cpe:2.3:a:ninenines:cowlib::::::::
ninenines	cowlib	Affected: f017f8a0ecbffd5033d9ab49bf180186f7a523a7 (git) cpe:2.3:a:ninenines:cowlib::::::::

Credits

Peter Ullrich

Show details on NVD website

JSON

To clipboard

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                  },
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                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-11T18:55:16.028478Z",
                "version": "2.0.3"
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            "cow_cookie"
          ],
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            "src/cow_cookie.erl"
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            {
              "name": "cow_cookie:cookie/1"
            }
          ],
          "repo": "https://github.com/ninenines/cowlib",
          "vendor": "ninenines",
          "versions": [
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          ],
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          "supportingMedia": [
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              "base64": false,
              "type": "text/html",
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            }
          ],
          "value": "The application must pass attacker-controlled bytes as cookie names or values to cow_cookie:cookie/1. Applications that construct cookie lists exclusively from trusted, application-controlled values are not affected."
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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                {
                  "criteria": "cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*",
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          "value": "Peter Ullrich"
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              "value": "\u003cp\u003eImproper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027) vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields.\u003c/p\u003e\u003cp\u003e\u003ctt\u003ecow_cookie:cookie/1\u003c/tt\u003e in cowlib builds a client-side \u003ctt\u003eCookie:\u003c/tt\u003e request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject \u003ctt\u003e;\u003c/tt\u003e, \u003ctt\u003e,\u003c/tt\u003e, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting \u003ctt\u003e; admin=1\u003c/tt\u003e to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (\u003ctt\u003eparse_cookie_name/1\u003c/tt\u003e, \u003ctt\u003eparse_cookie_value/1\u003c/tt\u003e) and \u003ctt\u003esetcookie/3\u003c/tt\u003e already validate and reject these characters; the encoder alone is missing the check.\u003c/p\u003e\u003cp\u003eThis issue affects cowlib from 2.9.0.\u003c/p\u003e"
            }
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          "value": "Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027) vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields.\n\ncow_cookie:cookie/1 in cowlib builds a client-side Cookie: request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject ;, ,, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting \"; admin=1\" to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (parse_cookie_name/1, parse_cookie_value/1) and setcookie/3 already validate and reject these characters; the encoder alone is missing the check.\n\nThis issue affects cowlib from 2.9.0."
        }
      ],
      "impacts": [
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          "capecId": "CAPEC-105",
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      ],
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            "attackRequirements": "PRESENT",
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            "userInteraction": "NONE",
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            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "LOW"
          },
          "format": "CVSS",
          "scenarios": [
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              "lang": "en",
              "value": "GENERAL"
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      "problemTypes": [
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          "descriptions": [
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              "cweId": "CWE-93",
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      "providerMetadata": {
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        }
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      "source": {
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      "title": "Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1",
      "workarounds": [
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          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
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  "cveMetadata": {
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  },
  "dataType": "CVE_RECORD",
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}

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

GHSA-G2WM-735Q-3F56

CVE-2026-43969 (GCVE-0-2026-43969)

Tags

Sightings

Nomenclature