CVE-2026-59980
hpack: Unbounded variable integer decoding can cause run-away computation on malformed input
- State
- Published
- Severity
- 6.3 Medium
- Published
- Sep 23, 2026
- Updated
- Sep 24, 2026
- Reserved
- Jul 7, 2026
Description
hpack is an HTTP/2 Header Encoding for Python. Prior to version 4.2.0, 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. A fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation. As a workaround, sanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 6.3 Medium | 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 | GitHub_M |
Weaknesses
- CWE-400 Uncontrolled Resource Consumption
Affected Products
| Product | Versions |
|---|---|
hpackpython-hyper |
|
References
- https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2
- 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
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