Get a Demo

Let's Patch It!

Book a short call with one our specialists, we'll walk you through how Endor Patches work, and ask you a few questions about your environment (like your primary programming languages and repository management). We'll also send you an email right after you fill out the form, feel free to reply with any questions you have in advance!

CVE

CVE-2026-34520

AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass
Back to all
CVE

CVE-2026-34520

AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass

Summary

The C parser (the default for most installs) accepted null bytes and control characters is response 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

Package Versions Affected

Package Version
patch Availability
No items found.

Automatically patch vulnerabilities without upgrading

Fix Without Upgrading
Detect compatible fix
Apply safe remediation
Fix with a single pull request

CVSS Version

Severity
Base Score
CVSS Version
Score Vector
C
H
U
2.7
-
4.0
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/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
C
H
U
0
-
C
H
U
-

Related Resources

No items found.

References

https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf, https://nvd.nist.gov/vuln/detail/CVE-2026-34520, https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4, https://github.com/aio-libs/aiohttp, https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4

Severity

9.1

CVSS Score
0
10

Basic Information

Ecosystem
Base CVSS
9.1
EPSS Probability
0.00045%
EPSS Percentile
0.13762%
Introduced Version
0
Fix Available
3.13.4,1.5.0.1-r1

Fix Critical Vulnerabilities Instantly

Secure your app without upgrading.
Fix Without Upgrading