Inefficient regular expression complexity in Twisted Web - #VU144313
Published: August 19, 2026
Vulnerability identifier: #VU144313
CSH Severity: Low
CVSS v4: 5.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to inefficient regular expression complexity in the wildcardToRegexp() function in twisted/mail/imap4.py when processing IMAP wildcard patterns in LIST or LSUB commands. A remote user can send a specially crafted quoted pattern string containing catastrophic-backtracking regex syntax to cause a denial of service.
Because the server uses a cooperative single-threaded reactor, a blocking regex match can freeze all I/O on the server for the duration of the match.
Affected software
Twisted Web
Remediation
Install security update from vendor's website.
Twisted Web - update to 26.4.0 rc1