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

CVE-2026-115877 is fixed in twisted on 1 platform by DEBIAN-CVE-2026-115877 (version 26.10.0-1), released November 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-115877
- Priority: Routine
- CVSS: 5.4 (Moderate)
- EPSS: 0.0026
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 23, 2026
- Weakness: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-115877

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | twisted Debian 14 | 26.10.0-1 | [DEBIAN-CVE-2026-115877](https://patchblox.com/security/data/fix/linux/debian-cve-2026-115877.md) | Nov 3, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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