Twisted has a Denial of Service (DoS) in twisted.names via Crafted DNS Compression Pointer Chains

Exploitation

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

CVSS

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

EPSS

• CVE-2026-42304: 0.43% estimated exploitation activity in the next 30 days; percentile 37.65 (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.

Details The twisted.names module is vulnerable to a Denial of Service (DoS) attack via resource exhaustion during DNS name decompression. A remote, unauthenticated attacker can exploit this by sending a crafted TCP DNS packet containing deeply chained compression pointers. This flaw bypasses previous loop-prevention logic, causing the single-threaded Twisted reactor to hang while processing millions of recursive lookups, effectively freezing the server. --- Technical Details The main issue is in twisted.names.dns.Name.decode. A visited set was added in 2011 (commit e11cd82) to prevent infinite loops, but there is still no limit on the number of pointer dereferences per message. Also, the visited set is reset for each Question record. Because DNSServerFactory handles every record in QDCOUNT without checking them, an attacker can add thousands of questions that all refer to the same long chain of pointers. This makes the parser repeat a complex and unnecessary search. --- PoC ---…

Published by the source

5 May 2026, 21:12 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:45 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-grgv-6hw6-v9g4

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-grgv-6hw6-v9g4

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# Patch Next advisory brief: CVE-2026-42304

Advisory: Twisted has a Denial of Service (DoS) in twisted.names via Crafted DNS Compression Pointer Chains
IDs: CVE-2026-42304, GHSA-grgv-6hw6-v9g4
Record: https://patchnext.com/advisories/cve-2026-42304 (revision 2, source checked 26 Oct 2026, 13:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: twisted 26.4.0rc2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI twisted: affected <= 25.5.0; fixed in 26.4.0rc2

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

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## 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://osv.dev/vulnerability/GHSA-grgv-6hw6-v9g4 (OSV record GHSA-grgv-6hw6-v9g4 lists affected ranges: PyPI twisted >=0 <26.4.0rc2 (fixed))
- Verified: https://github.com/advisories/GHSA-grgv-6hw6-v9g4 (GitHub-reviewed advisory GHSA-grgv-6hw6-v9g4 lists affected ranges: PyPI twisted >=0 <=25.5.0)

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