CVE-2026-59980
hpack: Unbounded variable integer decoding can cause run-away computation on malformed input
CVSS Score
0.0
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-400 |
| Vendor | python-hyper |
| Product | hpack |
| Published | Sep 23, 2026 |
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Affected Versions
python-hyper / hpack
< 4.2.0
References
github.com: https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2 github.com: https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c cs.opensource.google: https://cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18a docs.rs: https://docs.rs/http2/0.5.19/src/http2/hpack/decoder.rs.html#403