GHSA-P88M-4JFJ-68FV

Vulnerability from github – Published: 2026-06-19 14:21 – Updated: 2026-06-19 14:21
VLAI
Summary
undici vulnerable to HTTP header injection via Set-Cookie percent-decoding
Details

Impact

undici's cookie parser in parseSetCookie percent-decodes cookie values via qsUnescape, turning encoded sequences like %0D%0A, %00, %3B, and %3D into their literal byte equivalents. RFC 6265 §5.4 does not specify any decoding and browsers do not decode either.

Applications that parse a Set-Cookie header and then forward the parsed value into a response header (proxies, middleware, SSR frameworks) become vulnerable to HTTP response header injection: an attacker-controlled upstream can inject arbitrary Set-Cookie, Location, or Cache-Control headers into the application's downstream response, enabling session fixation, open redirect, or cache poisoning.

Affected applications are those that use undici's cookie parsing (parseSetCookie, parseCookie, getSetCookies) and forward the parsed cookie value into a response header.

This was introduced in undici 7.0.0 via #3789.

Patches

Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.

Workarounds

If upgrade is not immediately possible, do not forward values returned by parseSetCookie/parseCookie/getSetCookies directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, ;, and = bytes.

Severity
5.9 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "undici"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.27.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "undici"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "7.0.0"
            },
            {
              "fixed": "7.28.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "undici"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "8.0.0"
            },
            {
              "fixed": "8.5.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-9679"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-93"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T14:21:30Z",
    "nvd_published_at": "2026-06-17T18:18:06Z",
    "severity": "MODERATE"
  },
  "details": "## Impact\n\nundici\u0027s cookie parser in `parseSetCookie` percent-decodes cookie values via `qsUnescape`, turning encoded sequences like `%0D%0A`, `%00`, `%3B`, and `%3D` into their literal byte equivalents. RFC 6265 \u00a75.4 does not specify any decoding and browsers do not decode either.\n\nApplications that parse a `Set-Cookie` header and then forward the parsed value into a response header (proxies, middleware, SSR frameworks) become vulnerable to HTTP response header injection: an attacker-controlled upstream can inject arbitrary `Set-Cookie`, `Location`, or `Cache-Control` headers into the application\u0027s downstream response, enabling session fixation, open redirect, or cache poisoning.\n\nAffected applications are those that use undici\u0027s cookie parsing (`parseSetCookie`, `parseCookie`, `getSetCookies`) and forward the parsed cookie value into a response header.\n\nThis was introduced in undici 7.0.0 via [#3789](https://github.com/nodejs/undici/pull/3789).\n\n## Patches\n\nUpgrade to undici v6.27.0, v7.28.0 or v8.5.0.\n\n## Workarounds\n\nIf upgrade is not immediately possible, do not forward values returned by `parseSetCookie`/`parseCookie`/`getSetCookies` directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, `;`, and `=` bytes.",
  "id": "GHSA-p88m-4jfj-68fv",
  "modified": "2026-06-19T14:21:30Z",
  "published": "2026-06-19T14:21:30Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nodejs/undici/security/advisories/GHSA-p88m-4jfj-68fv"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-9679"
    },
    {
      "type": "WEB",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nodejs/undici"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "undici vulnerable to HTTP header injection via Set-Cookie percent-decoding"
}


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