# CVE-2026-115774: Twisted IMAP4 server denial of service via negative literal size

Source: https://junglewise.ai/threats/cve-2026-115774-twisted-denial-of-service-in-the-twisted-imap4-server-via-a  
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-2026-115774 · Severity: medium · CVSS 4.9 · Published 2026-10-23

Twisted is a networking library commonly used to build email servers supporting IMAP, SMTP, and other protocols. An authenticated user can freeze the entire mail server process by sending a specially crafted SEARCH command, causing all connected clients to stop being served until the process is manually restarted. The attack requires valid login credentials but needs only one small command to take down the whole service.

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-2026-115774 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-115774 being exploited in the wild.

**How severe is CVE-2026-115774?** Medium severity, with a CVSS score of 4.9, 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-2026-115774?** 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-2026-115774 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-115774?** 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 IMAP4 parser in twisted.mail.imap4.parseNestedParens fails to validate that literal sizes are non-negative, allowing a negative value like {-100} to drive the cursor backward and wrap around due to Python's negative indexing semantics. This causes an infinite loop in the synchronous parser that blocks the single-threaded reactor thread indefinitely. The vulnerability is reachable from the SEARCH command after successful login and mailbox selection, requiring only standard authentication.

## Affected products

- Twisted Twisted 26.4.0 and earlier

## Identifiers

- CVE-2026-115774
- GHSA-2qrf-pqgx-qh9v

## Timeline

- 2026-10-23: disclosed

## Related threats

- [Twisted HTTP/2 server denial of service via rapid stream reset](https://junglewise.ai/threats/twisted-unauthenticated-remote-denial-of-service-in-the-twisted-http-2-0f2d7a0e)
- [Twisted: DNS Response Spoofing in twisted.names Due to Missing Source Address Validation](https://junglewise.ai/threats/cve-2026-83813-twisted-is-an-event-based-framework-for-internet-applications)
- [Twisted HTTP request smuggling via bare CR or LF in header](https://junglewise.ai/threats/cve-2026-115877-twisted-http-request-smuggling-in-twisted-web-via-a-bare-cr-or)
- [Twisted conch telnet unbounded subnegotiation buffer denial of service](https://junglewise.ai/threats/cve-2026-115778-twisted-unauthenticated-remote-denial-of-service-in-the-twisted)
- [Twisted is an event-based framework for internet applications, supporting Python 3.6+. Prior to 26.10.0rc1, twisted.words.protocols.irc.IRC.](https://junglewise.ai/threats/cve-2026-115776-twisted-unauthenticated-remote-denial-of-service-in-the-twisted)