{"id":"CVE-2026-59980","aliases":["GHSA-8v8h-hg4w-mvq2","PYSEC-2026-4053"],"url":"https://o3.security/vulnerability/CVE-2026-59980","summary":"hpack: Unbounded variable integer decoding can cause run-away computation on malformed input","details":"### Impact\n\nUsers 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.\n\n### Patches\nA fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation.\n\n### Workarounds\nSanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.","published":"2026-09-23T22:07:35.095Z","modified":"2026-10-22T11:56:54.920684461Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"hpack","fixedVersion":"4.2.0"}],"fix":{"url":"https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c","label":"python-hyper/hpack@8cfb02c"},"references":[{"type":"WEB","url":"https://cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18a"},{"type":"WEB","url":"https://docs.rs/http2/0.5.19/src/http2/hpack/decoder.rs.html#403"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59980.json"},{"type":"ADVISORY","url":"https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-59980"},{"type":"FIX","url":"https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c"},{"type":"PACKAGE","url":"https://github.com/python-hyper/hpack"},{"type":"WEB","url":"https://github.com/python-hyper/hpack/releases/tag/v4.2.0"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-22T11:56:54.920684461Z"}}