GitHub Advisoryadvisory · PyPI
GHSA-8v8h-hg4w-mvq2 hpack: Unbounded variable integer decoding can cause run-away computation on malformed input
MEDIUM
Official page ↗
- Aliases
- CVE-2026-59980
- Ecosystem
- PyPI
- Packages
- hpack
- Severity
- Moderate
- CVSS vector
- CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- Weaknesses
- CWE-400
- Reviewed
- 2026-09-24
Affected packages
• PyPI hpack: < 4.2.0 → fixed in 4.2.0
Description
Impact
Users of the python-hyper/hpack library, most commonly used as downstream dependency of the python-hyper/h2 library (an HTTP/2 client and server implementation). Unbounded variable integer decoding can cause run-away computation on malformed input leading to O(n^2) runtime, effectively blocking further processing with large enough unsanitized input.
Patches
A fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation.
Workarounds
Sanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.
Related
Alias · CVE (1)
- CVE-2026-59980 hpack is an HTTP/2 Header Encoding for Python. vulnerability
Weakness · CWE (1)
- CWE-400 Uncontrolled Resource Consumption weakness
References
- https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2 web
- https://nvd.nist.gov/vuln/detail/CVE-2026-59980 advisory
- https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c web
- https://cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18a web
- https://docs.rs/http2/0.5.19/src/http2/hpack/decoder.rs.html#403 web
- https://github.com/python-hyper/hpack package
- https://github.com/python-hyper/hpack/releases/tag/v4.2.0 web