CVE-2026-115877: Request Smuggling (CVSS 5.4)

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.

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CVSS v3.1 Score

5.4

MEDIUM

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

Weakness Type (CWE)

CWE-444 CWE-444

References

Other References

https://github.com/twisted/twisted/commit/022b6f7feb5980166c71f54e2c0d8f4f21ff6e1a https://github.com/twisted/twisted/commit/1616f702d36eda8990a5a5b22ad70fab140a7eb1 https://github.com/twisted/twisted/pull/12755 https://github.com/twisted/twisted/releases/tag/twisted-26.10.0rc1 https://github.com/twisted/twisted/security/advisories/GHSA-q7qq-6mhp-9rc4

Frequently Asked Questions

What is CVE-2026-115877? +

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. It has a CVSS v3.1 base score of 5.4 (MEDIUM).

How severe is CVE-2026-115877? +

CVE-2026-115877 has a CVSS v3.1 score of 5.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

How do I check if I'm vulnerable to CVE-2026-115877? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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