# CVE-2026-115778: Twisted: Unauthenticated Remote Denial of Service in the Twisted conch Telnet Transport via an Unbounded Subnegotiation Buffer

CVE-2026-115778 is fixed in twisted on 1 platform by DEBIAN-CVE-2026-115778 (version 26.10.0-1), released November 3, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-115778
- Priority: High
- CVSS: 7.5 (Moderate)
- EPSS: 0.0054
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 23, 2026
- Weakness: Uncontrolled Resource Consumption
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-115778

## Description

Twisted is an event-based framework for internet applications, supporting Python 3.6+. Prior to 26.10.0rc1, twisted.conch.telnet.Telnet.dataReceived appends every byte received after IAC SB to a persistent subnegotiation buffer until IAC SE is received, without applying a maximum length. Telnet option negotiation occurs before authentication, so an unauthenticated peer can omit the terminator and continuously grow the buffer. The resulting memory exhaustion can terminate the process and every service it hosts. 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-2026-115778](https://patchblox.com/security/data/fix/linux/debian-cve-2026-115778.md) | Nov 3, 2026 |

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Data as of 2026-11-09T07:25:28Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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