Twisted: IMAP wildcardToRegexp() ReDoS

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2026-106454: 0.42% estimated exploitation activity in the next 30 days; percentile 36.01 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary wildcardToRegexp() in twisted/mail/imap4.py converts IMAP LIST/LSUB wildcard patterns to Python regular expressions. It substitutes the two IMAP wildcards ( → (?:.?) and % → (?:(?:[^\\/])?)) but passes every other character through unchanged to re.compile(). This means that an authenticated IMAP client can send a quoted pattern string containing arbitrary regex syntax - including catastrophic-backtracking constructs such as (a+)+z. Because Twisted runs a cooperative, single-threaded reactor, a blocking regex match freezes all I/O on the server for the duration of the match. --- Vulnerable Code twisted/mail/imap4.py --- Proof of Concept Output on Twisted 25.5.0: Timing doubles roughly every two characters (exponential growth), confirming catastrophic backtracking. --- Impact Twisted's reactor is single-threaded and cooperative. A blocking re.match() call suspends the entire event loop - no other connection can be accepted, read, or written while the match runs. A single…

Published by the source

7 Oct 2026, 16:18 UTC

Last modified by the source

15 Oct 2026, 14:56 UTC

Source last checked

26 Oct 2026, 13:55 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-8pqf-f4m5-798g

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-8pqf-f4m5-798g

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-8pqf-f4m5-798g

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# Patch Next advisory brief: CVE-2026-106454

Advisory: Twisted: IMAP wildcardToRegexp() ReDoS
IDs: CVE-2026-106454, GHSA-8pqf-f4m5-798g
Record: https://patchnext.com/advisories/cve-2026-106454 (revision 3, source checked 26 Oct 2026, 13:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI twisted: affected <= 26.4.0

## Suggested inspection (read-only)
- `python -m pip show twisted`: prints the installed version. Run with the environment that serves production active.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on twisted.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-8pqf-f4m5-798g (GitHub-reviewed advisory GHSA-8pqf-f4m5-798g lists affected ranges: PyPI twisted >=0 <=26.4.0)
- Verified: https://osv.dev/vulnerability/GHSA-8pqf-f4m5-798g (OSV record GHSA-8pqf-f4m5-798g lists affected ranges: PyPI twisted >=0 <=26.4.0)

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