aiohttp's HTTP parser (the python one, not llhttp) still overly lenient about separators
Summary
Security-sensitive parts of the Python HTTP parser retained minor differences in allowable character sets, that must trigger error handling to robustly match frame boundaries of proxies in order to protect against injection of additional requests. Additionally, validation could trigger exceptions that were not handled consistently with processing of other malformed input.
Details
These problems are rooted in pattern matching protocol elements, previously improved by PR #3235 and GHSA-gfw2-4jvh-wgfg:
-
The expression
HTTP/(\d).(\d)lacked another backslash to clarify that the separator should be a literal dot, not just any Unicode code point (result:HTTP/(\d)\.(\d)). -
The HTTP version was permitting Unicode digits, where only ASCII digits are standards-compliant.
-
Distinct regular expressions for validating HTTP Method and Header field names were used - though both should (at least) apply the common restrictions of rfc9110
token.
PoC
GET / HTTP/1ö1
GET / HTTP/1.𝟙
GET/: HTTP/1.1
Content-Encoding?: chunked
Impact
Primarily concerns running an aiohttp server without llhttp:
- behind a proxy: Being more lenient than internet standards require could, depending on deployment environment, assist in request smuggling.
- directly accessible or exposed behind proxies relaying malformed input: the unhandled exception could cause excessive resource consumption on the application server and/or its logging facilities.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | aiohttp | < 3.9.2 | 3.9.2 |
References
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-8qpw-xqxj-h4r2
- https://github.com/aio-libs/aiohttp/pull/8074
- https://github.com/aio-libs/aiohttp/commit/33ccdfb0a12690af5bb49bda2319ec0907fa7827
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/XXWVZIVAYWEBHNRIILZVB3R3SDQNNAA7/
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-gfw2-4jvh-wgfg
- https://nvd.nist.gov/vuln/detail/CVE-2024-23829
- https://github.com/aio-libs/aiohttp/pull/3235
- https://github.com/aio-libs/aiohttp/pull/8074/files
- https://github.com/aio-libs/aiohttp
- https://github.com/pypa/advisory-database/tree/main/vulns/aiohttp/PYSEC-2024-26.yaml
- https://lists.debian.org/debian-lts-announce/2025/02/msg00002.html
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ICUOCFGTB25WUT336BZ4UNYLSZOUVKBD
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/XXWVZIVAYWEBHNRIILZVB3R3SDQNNAA7
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L- Weakness (CWE)
CWE-444- Platform
- Python (PyPI)
- Package
aiohttp- Disclosed
- 29.01.2024
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2024-26 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-8qpw-xqxj-h4r2 - CC BY 4.0
Vulnerability history: aiohttp
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 55
- First → latest
- 02.2021 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 7
- Medium 29
- Low 19
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 6
- 2024: 7
- 2025: 1
- 2026: 40
-
aiohttp's HTTP parser (the python one, not llhttp) still overly lenient about separators this entry
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