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Critical 1 vendor · 1 advisory

CVE-2026-34520: AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass

CVE-2026-34520 key facts

CISA KEV
Not listed (catalogue checked )
Highest advisory rating
Critical
CVSS vector
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 · base score 2.7, scored by GitHub_MAttack vector: network. Attack complexity: low. Attack requirements: none. Privileges required: none. User interaction: none. Confidentiality impact on the vulnerable system: none. Integrity impact on the vulnerable system: low. Availability impact on the vulnerable system: none. Confidentiality impact on subsequent systems: none. Integrity impact on subsequent systems: none. Availability impact on subsequent systems: none.
Weakness
  • CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
EPSS
0.48% chance of exploitation in the next 30 days (41st percentile). FIRST EPSS, .
CISA SSVC
Exploitation: none observed. Automatable: yes. Technical impact: partial. CISA, .
Vendor advisories
1 from Splunk
Assigned by
GitHub_M (CNA)
CVE record published
Listed by VulniPulse

Ratings, versions and fixes are quoted from the vendor advisories that cover only CVE-2026-34520; each belongs to its advisory, not to every product listed. How records are collected and checked.

Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4.

Text from the CVE.org record (GitHub_M).

Vendor advisories for CVE-2026-34520

Splunk

1 advisory
  • Advisory severityCritical

    Critical [CVE-2025-13465 +86] Third-Party Package Updates in Splunk SOAR - August 2026

    SVD-2026-0805Source published

    This bulletin covers 87 CVEs. The products, versions, score and guidance below describe the bulletin; check its source for applicability to this specific CVE.

    Splunk remedied common vulnerabilities and exposures (CVEs) in Third Party Packages in Splunk SOAR version 8.6.0, and higher. Affected product named by the advisory: Splunk SOAR 8.6.

    Affected products in this advisory
    • Splunk SOAR 8.6
    Source-reported affected versions
    • Splunk SOAR Below 8.6.0
    Source-reported fixed versions
    • Splunk SOAR 8.6.0
    Mitigation guidance
    • Upgrade Splunk SOAR to version 8.6.0, or higher.
    Full advisory and evidenceOpen source bulletin

References

Timeline

  1. CVE record published
  2. CVE record last updated
  3. First vendor advisory listed by VulniPulse

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