PYSEC-2026-4053
See a problem?- Import Source
- https://github.com/pypa/advisory-database/blob/main/vulns/hpack/PYSEC-2026-4053.yaml
- JSON Data
- https://api.osv.dev/v1/vulns/PYSEC-2026-4053
- Aliases
- Published
- 2026-10-01T16:38:39Z
- Modified
- 2026-10-01T17:45:03Z
- Severity
-
- 6.3 (Medium) CVSS_V4 - 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 CVSS Calculator
- Summary
- hpack: Unbounded variable integer decoding can cause run-away computation on malformed input
- Details
-
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
0xFFvalues to prevent malicious use. - References
-
- https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2
- https://nvd.nist.gov/vuln/detail/CVE-2026-59980
- https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c
- https://cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18a
- https://docs.rs/http2/0.5.19/src/http2/hpack/decoder.rs.html#403
- https://github.com/python-hyper/hpack
- https://github.com/python-hyper/hpack/releases/tag/v4.2.0
- https://pypi.org/project/hpack
- https://github.com/advisories/GHSA-8v8h-hg4w-mvq2
Affected packages
PyPI / hpack
Package
- Name
- hpack
- View open source insights on deps.dev
- Purl
- pkg:pypi/hpack
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0 Unknown introduced version / All previous versions are affectedFixed4.2.0