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CVE-2026-34520
AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass
Low2.7EPSS 0.48%
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 4.0 | Low2.7 | 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 |
| CISA-ADPADP (enrichment) | 3.1 | Critical9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H |
| NVDNVD · Analyzed | 4.0 | Low2.7 | 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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
- EPSS (exploitation in 30 days)
- 0.48% · top 58% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
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The list uses the assigner's score when there is one, then CISA's, then NVD's: Low 2.7.
Weakness
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- PyPIaiohttpGHSA-63hf-3vf5-4wqf (opens in a new tab)
References (3)
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf (opens in a new tab)x_refsource_CONFIRM
- https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4 (opens in a new tab)x_refsource_MISC
- https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-63hf-3vf5-4wqf (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-34520)Record last updated .