# CVE-2026-115877: Twisted HTTP request smuggling via bare CR or LF in header

Source: https://junglewise.ai/threats/cve-2026-115877-twisted-http-request-smuggling-in-twisted-web-via-a-bare-cr-or  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-23. Updated: 2026-10-23  
License: CC BY 4.0 with a link back

CVE-2026-115877 · Severity: medium · CVSS 5.4 · Published 2026-10-23

Twisted, a Python networking library used in web servers and proxies, fails to reject bare carriage return or line feed characters in HTTP header values. An attacker can exploit this to smuggle requests past front-end security controls, bypass access restrictions, poison shared connections, or poison web caches when Twisted sits behind a proxy that interprets line breaks differently.

Technologies: [twisted (PyPI)](https://junglewise.ai/threats/technologies/pypi-twisted), [Twisted](https://junglewise.ai/threats/technologies/twisted-twisted). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi), [Twisted](https://junglewise.ai/threats/vendors/twisted).

## Quick answers

**Is CVE-2026-115877 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-115877 being exploited in the wild.

**How severe is CVE-2026-115877?** Medium severity, with a CVSS score of 5.4, published 23 October 2026.

**Which products and versions are affected?** twisted (PyPI) <= 26.4.0, ECOSYSTEM:introduced=0,fixed=26.10.0rc1; Twisted 26.4.0 and earlier.

**Is there a fix for CVE-2026-115877?** Yes. twisted (PyPI): upgrade to 26.10.0rc1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-115877 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-115877?** Check whether you run twisted (PyPI) or Twisted at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- twisted (PyPI): upgrade to 26.10.0rc1 or later

  ```sh
  pip install "twisted>=26.10.0rc1"
  ```


## Technical details

The vulnerability is an incomplete header validation (CWE-444) in HTTPChannel.headerReceived, which rejects NUL bytes but not bare CR or LF characters in header values. When a bare LF appears in a header value, the parser treats the next header as part of the value, causing request framing disagreement with front-end proxies. An attacker sends a crafted request with a bare LF in a header, followed by a second hidden request body; the front-end frames it one way while Twisted frames it another, allowing request smuggling past access controls or connection poisoning.

## Affected products

- Twisted Twisted 26.4.0 and earlier

## Identifiers

- CVE-2026-115877
- GHSA-q7qq-6mhp-9rc4

## Timeline

- 2026-10-23: disclosed

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