# CVE-2026-115778: Twisted conch telnet unbounded subnegotiation buffer denial of service

Source: https://junglewise.ai/threats/cve-2026-115778-twisted-unauthenticated-remote-denial-of-service-in-the-twisted  
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-2026-115778 · Severity: high · CVSS 7.5 · Published 2026-10-23

Twisted is a Python library that provides network protocol implementations, including telnet support. An unauthenticated attacker can send specially crafted telnet commands to exhaust server memory and cause a denial of service, taking down not only the telnet service but potentially all services on the same host.

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-2026-115778 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-115778 being exploited in the wild.

**How severe is CVE-2026-115778?** High severity, with a CVSS score of 7.5, 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 likely earlier versions.

**Is there a fix for CVE-2026-115778?** Yes. twisted (PyPI): upgrade to 26.10.0rc1 or later. Until then: Restrict network access to telnet and manhole transports to trusted peers only, or disable the telnet transport if it is not required for operations. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-115778 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-115778?** 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"
  ```


Restrict network access to telnet and manhole transports to trusted peers only, or disable the telnet transport if it is not required for operations.

## Technical details

A lack of length validation in the telnet subnegotiation parser (CWE-770) allows an unauthenticated remote peer to append an unbounded number of bytes to an in-memory buffer. The attack occurs at the transport layer before authentication by sending IAC SB (telnet subnegotiation begin) followed by continuous non-IAC bytes without ever sending IAC SE (subnegotiation end), causing the buffer to grow with each received byte until process memory is exhausted.

## Affected products

- Twisted Twisted 26.4.0 and likely earlier versions

## Identifiers

- CVE-2026-115778
- GHSA-cwm5-jh59-mwxr

## 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 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)
- [Twisted unbounded element tree denial of service](https://junglewise.ai/threats/cve-2026-115775-twisted-unauthenticated-remote-denial-of-service-in-the-twisted)