Medium severityNVD Advisory· Published Sep 23, 2026· Updated Sep 30, 2026
CVE-2026-59980
CVE-2026-59980
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.
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Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
hpackPyPI | < 4.2.0 | 4.2.0 |
Affected products
2- Range: <4.2.0
Patches
Vulnerability mechanics
References
7- github.com/advisories/GHSA-8v8h-hg4w-mvq2ghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-59980ghsaADVISORY
- cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18anvdWEB
- docs.rs/http2/0.5.19/src/http2/hpack/decoder.rs.htmlnvdWEB
- github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2cnvdWEB
- github.com/python-hyper/hpack/releases/tag/v4.2.0ghsaWEB
- github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2nvdWEB
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