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CVE-2026-34520VulnerabilityPublished Updated

Ansible: AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header

Affects ansibleSource GCVE Database

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Authoritative record:CVE-2026-34520· Low 2.7

Not known to be exploited · CVSS 2.7 Low : upgrade to 14.3.0 when convenient.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score
2.7Low
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 14.3.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 1 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade ansible to 14.3.0.

Affected software

ProductAffectedFixed in
Homebrewansiblepkg:brew/ansibleOther threatsAffected
  • <14.3.0
Fixed in
  • 14.3.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Summary The C parser (the default for most installs) accepted null bytes and control characters in request headers. ### Impact An attacker could send header values that are interpreted differently than expected due to the presence of control characters. For example, `request.url.origin()` may return a different value than the raw Host header, or what a reverse proxy interpreted it as., potentially resulting in some kind of security bypass. ----- Patch: https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4

References

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