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GHSA-R53P-7PC4-XJ5R

Vulnerability from github – Published: 2026-09-29 18:22 – Updated: 2026-09-29 18:22

Summary

undici vulnerable to downstream response splitting via retry interceptor

Details

Impact

Undici's interceptors.retry() can resume a request after a partial response and append the resumed bytes to an already partially delivered body, while the application still receives the original response's status and headers. When that response carried a Content-Length, the application can receive a longer body. Applications that forward Undici's status, headers, and body downstream without recalculating framing, for example proxy or gateway applications, may emit a response whose body exceeds the forwarded Content-Length, and the excess bytes can be read as the start of a subsequent HTTP response (downstream response splitting or desynchronization).

For example, a 404 Not Found with Content-Length: 2 that sends one byte then closes can be resumed with an open-ended Range request, and the resumed 206 Partial Content bytes are appended, so the application receives more than two body bytes while still seeing Content-Length: 2. The bug requires interceptors.retry() enabled, an attacker-controlled or faulty upstream, and a downstream forwarder that does not recalculate Content-Length.

Patches

Patched in undici v6.28.1, v7.29.1, and v8.10.2. Upgrade to one of these or later.

Workarounds

Disable interceptors.retry() for untrusted upstreams, or set maxRetries: 0.
Remove or recalculate Content-Length before forwarding a response body assembled by Undici.

Severity

3.7 (Low)


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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "undici"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.28.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "undici"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "7.0.0"
            },
            {
              "fixed": "7.29.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "undici"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "8.0.0"
            },
            {
              "fixed": "8.10.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-18540"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-444"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-29T18:22:07Z",
    "nvd_published_at": "2026-09-04T18:17:50Z",
    "severity": "LOW"
  },
  "details": "### Impact\n\nUndici\u0027s `interceptors.retry()` can resume a request after a partial response and append the resumed bytes to an already partially delivered body, while the application still receives the original response\u0027s status and headers. When that response carried a `Content-Length`, the application can receive a longer body. Applications that forward Undici\u0027s status, headers, and body downstream without recalculating framing, for example proxy or gateway applications, may emit a response whose body exceeds the forwarded `Content-Length`, and the excess bytes can be read as the start of a subsequent HTTP response (downstream response splitting or desynchronization).\n\nFor example, a `404 Not Found` with `Content-Length: 2` that sends one byte then closes can be resumed with an open-ended `Range` request, and the resumed `206 Partial Content` bytes are appended, so the application receives more than two body bytes while still seeing `Content-Length: 2`. The bug requires `interceptors.retry()` enabled, an attacker-controlled or faulty upstream, and a downstream forwarder that does not recalculate `Content-Length`.\n\n### Patches\n\nPatched in undici v6.28.1, v7.29.1, and v8.10.2. Upgrade to one of these or later.\n\n### Workarounds\n\n- Disable `interceptors.retry()` for untrusted upstreams, or set `maxRetries: 0`.\n- Remove or recalculate `Content-Length` before forwarding a response body assembled by Undici.",
  "id": "GHSA-r53p-7pc4-xj5r",
  "modified": "2026-09-29T18:22:07Z",
  "published": "2026-09-29T18:22:07Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nodejs/undici/security/advisories/GHSA-r53p-7pc4-xj5r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-18540"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nodejs/undici/commit/0160a719063fb0a77f4fdf9500b9166b91e14329"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nodejs/undici/commit/cd8af90b38ae33c2838d54a2d629774122effe95"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nodejs/undici/commit/ce31bc824b578008faae5d3350da66c1b5f71548"
    },
    {
      "type": "WEB",
      "url": "https://hackerone.com/reports/3900104"
    },
    {
      "type": "WEB",
      "url": "https://hackerone.com/reports/3900615"
    },
    {
      "type": "WEB",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nodejs/undici"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nodejs/undici/releases/tag/v6.28.1"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nodejs/undici/releases/tag/v7.29.1"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nodejs/undici/releases/tag/v8.10.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "undici vulnerable to downstream response splitting via retry interceptor"
}

CVE-2026-18540 (GCVE-0-2026-18540)

Vulnerability from cvelistv5 – Published: 2026-09-04 17:15 – Updated: 2026-09-04 17:50

Title

undici vulnerable to downstream response splitting via retry interceptor

Summary

undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an earlier partial response while still presenting the original response's status and headers. This happens when an upstream server delivers part of a body without a trustworthy resume checkpoint, for example a non-success response whose headers were already sent or a partial-content response with an unusable content range, then closes the connection and answers the resumed range request with more bytes. As a result the response body can be longer than the Content-Length that the application observes. An application that relays such a response to a downstream HTTP/1.1 peer without normalizing the framing can emit a body that exceeds the forwarded Content-Length, and the excess bytes can be interpreted as the start of a following response, which enables downstream response splitting or desynchronization. Exploitation requires an attacker-controlled upstream server and an application that forwards the response through a framing-sensitive path. This affects undici versions before 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.

Severity

3.7 (Low)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-04 17:50 UTC

CWE

CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Assigner

openjs redhat root Scorecard

References

2 references

URL	Tags
https://github.com/nodejs/undici/security/advisor…
https://cna.openjsf.org/security-advisories.html

Impacted products

1 product

Vendor	Product	Version
undici	undici	Affected: 0 , < 6.28.1 (semver) Unaffected: 6.28.1 (semver) Affected: 7.0.0 , < 7.29.1 (semver) Unaffected: 7.29.1 (semver) Affected: 8.0.0 , < 8.10.2 (semver) Unaffected: 8.10.2 (semver)

Credits

samuel871211 mcollina UlisesGascon

Show details on NVD website

JSON

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Sightings

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Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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