CVE-2026-1525 (GCVE-0-2026-1525)

Vulnerability from cvelistv5 – Published: 2026-03-12 19:56 – Updated: 2026-03-12 20:46
VLAI
Title
undici is vulnerable to Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Summary
Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple conflicting Content-Length values on the wire. Who is impacted: * Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as flat arrays * Applications that accept user-controlled header names without case-normalization Potential consequences: * Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-Length headers (400 Bad Request) * HTTP Request Smuggling: In deployments where an intermediary and backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential hijacking
Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
SSVC
Exploitation: poc Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-03-12 20:44 UTC
CWE
  • CWE-444 - Inconsistent interpretation of HTTP requests ('HTTP Request/Response smuggling')
Assigner
References
Impacted products
Vendor Product Version CPE status
undici undici Affected: < 6.24.0; 7.0.0 < 7.24.0
Unaffected: 6.24.0: 7.24.0
guessed Create a notification for this product.
Credits
Matteo Collina Ulises Gascón
Show details on NVD website
To clipboard 

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This produces malformed HTTP/1.1 requests with multiple conflicting\\u00a0Content-Length\\u00a0values on the wire.\\n\\nWho is impacted:\\n\\n  *  Applications using\\u00a0undici.request(),\\u00a0undici.Client, or similar low-level APIs with headers passed as flat arrays\\n  *  Applications that accept user-controlled header names without case-normalization\\n\\n\\nPotential consequences:\\n\\n  *  Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate\\u00a0Content-Length\\u00a0headers (400 Bad Request)\\n  *  HTTP Request Smuggling: In deployments where an intermediary and backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential hijacking\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eUndici allows duplicate HTTP\u0026nbsp;\u003ccode\u003eContent-Length\u003c/code\u003e\u0026nbsp;headers when they are provided in an array with case-variant names (e.g.,\u0026nbsp;\u003ccode\u003eContent-Length\u003c/code\u003e\u0026nbsp;and\u0026nbsp;\u003ccode\u003econtent-length\u003c/code\u003e). This produces malformed HTTP/1.1 requests with multiple conflicting\u0026nbsp;\u003ccode\u003eContent-Length\u003c/code\u003e\u0026nbsp;values on the wire.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eWho is impacted:\u003c/strong\u003e\u003c/p\u003e\u003cul\u003e\u003cli\u003eApplications using\u0026nbsp;\u003ccode\u003eundici.request()\u003c/code\u003e,\u0026nbsp;\u003ccode\u003eundici.Client\u003c/code\u003e, or similar low-level APIs with headers passed as flat arrays\u003c/li\u003e\u003cli\u003eApplications that accept user-controlled header names without case-normalization\u003c/li\u003e\u003c/ul\u003e\u003cp\u003e\u003cstrong\u003ePotential consequences:\u003c/strong\u003e\u003c/p\u003e\u003cul\u003e\u003cli\u003e\u003cstrong\u003eDenial of Service\u003c/strong\u003e: Strict HTTP parsers (proxies, servers) will reject requests with duplicate\u0026nbsp;\u003ccode\u003eContent-Length\u003c/code\u003e\u0026nbsp;headers (400 Bad Request)\u003c/li\u003e\u003cli\u003e\u003cstrong\u003eHTTP Request Smuggling\u003c/strong\u003e: In deployments where an intermediary and backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential hijacking\u003c/li\u003e\u003c/ul\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-444\", \"description\": \"CWE-444 Inconsistent interpretation of HTTP requests (\u0027HTTP Request/Response smuggling\u0027)\"}]}], \"providerMetadata\": {\"orgId\": \"ce714d77-add3-4f53-aff5-83d477b104bb\", \"shortName\": \"openjs\", \"dateUpdated\": \"2026-03-12T19:56:55.092Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-1525\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-03-12T20:46:13.379Z\", \"dateReserved\": \"2026-01-28T12:04:51.369Z\", \"assignerOrgId\": \"ce714d77-add3-4f53-aff5-83d477b104bb\", \"datePublished\": \"2026-03-12T19:56:55.092Z\", \"assignerShortName\": \"openjs\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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.


Detection rules are retrieved from Rulezet.