CVE-2025-43859: Yewtube · h11 accepts some malformed Chunked-Encoding bodies
Affects yewtubeSource GCVE Database
Not known to be exploited · CVSS 9.1 Critical : upgrade to 2.12.1_1 as a priority.
Data as of 30 Oct 2026, 05:16 UTC
- Patch
- Available – fixed in 2.12.1_1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NExploitation evidence
Disclosed: evidence found.
CVE published 13 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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 yewtube to 2.12.1_1.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Homebrewyewtubepkg:brew/yewtubeOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available in h11 version 0.15.0 that corrects the parsing of chunked bodies. Since exploitation requires both h11 and a buggy proxy, fixing either component fully mitigates the issue. Users should upgrade h11 to 0.15.0 or later. No additional mitigations are required if the patch is applied.
Description
A vulnerability in h11's handling of HTTP/1.1 chunked transfer encoding allows malformed chunked bodies to be accepted due to lenient parsing of trailing line terminators. This can lead to HTTP request smuggling when combined with a proxy that parses chunked bodies differently. The issue is fixed in h11 version 0.15.0. Exploitation requires both h11 and a buggy proxy component, so fixing either mitigates the risk.
References
- github.com/python-hyper/h11/security/advisories/GHSA-vqfr-h8mv-ghfj (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2025-43859 (opens in a new tab)
- github.com/python-hyper/h11/commit/114803a29ce50116dc47951c690ad4892b1a36ed (opens in a new tab)
- github.com/pypa/advisory-database/tree/main/vulns/h11/PYSEC-2026-348.yaml (opens in a new tab)
- github.com/python-hyper/h11 (opens in a new tab)
- pypi.org/project/h11 (opens in a new tab)