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Vulnerability · Published Oct 23, 2026 · Assigned by GitHub_M

CVE-2026-115877Twisted: HTTP Request Smuggling in twisted.web via a Bare CR or LF in a Header Value

Medium 5.4

In plain English

A medium-severity security flaw in twisted from twisted. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.4Medium
Exploit odds (30 days)0.3%top 82.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official description

Twisted is an event-based framework for internet applications, supporting Python 3.6+. Prior to 26.10.0rc1, twisted.web.http.HTTPChannel.headerReceived rejects a NUL byte in an HTTP header value but accepts a bare carriage return or bare line feed. Because Twisted splits header lines only on CRLF, a hidden Content-Length header can remain folded into another value while a lenient front end treats the bare character as a line terminator. The resulting framing disagreement can smuggle a following request past front-end access controls, poison a shared connection or cache, and expose a later client to the wrong response. This issue is an incomplete-fix residual of earlier Twisted request-smuggling protections. This issue is fixed in version 26.10.0rc1.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12twistedno fix listedDEBIAN-CVE-2026-115877
Debian:13twistedno fix listedDEBIAN-CVE-2026-115877
Debian:14twisted26.10.0-1DEBIAN-CVE-2026-115877
PyPItwisted26.10.0rc1GHSA-q7qq-6mhp-9rc4
Ubuntu:22.04:LTStwistedno fix listedUBUNTU-CVE-2026-115877
Ubuntu:24.04:LTStwistedno fix listedUBUNTU-CVE-2026-115877
Ubuntu:26.04:LTStwistedno fix listedUBUNTU-CVE-2026-115877
Ubuntu:26.10twistedno fix listedUBUNTU-CVE-2026-115877

Affected products (as reported)

VendorProductVersions
twisted twisted < 26.10.0rc1

Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N

References