What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-23 · updated 2026-10-26
• Weakness: CWE-400

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.

Affected products

• twisted: before 26.10.0rc1

References

• https://github.com/twisted/twisted/commit/073ba878c6c07d569cb61abc5ae76d46eff1b529
• https://github.com/twisted/twisted/commit/5d91cc66a3591faba758a80a1479e0103602facc
• https://github.com/twisted/twisted/pull/12750
• https://github.com/twisted/twisted/releases/tag/twisted-26.10.0rc1
• https://github.com/twisted/twisted/security/advisories/GHSA-cwm5-jh59-mwxr

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