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

Vulnerability summary

CVE-2026-115774 is a medium (CVSS 4.9) Uncontrolled Resource Consumption vulnerability in twisted. EPSS estimates a 0.52% chance of exploitation in the next 30 days, higher than 44.2% of scored vulnerabilities.

Timeline

1. 23-10-2026
   PublishedVulnerability first disclosed.
2. 29-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.
• CWE-835Loop with Unreachable Exit ConditionThe product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.