{"cve":"CVE-2026-59980","nvd":{"published":"2026-09-23T23:17:11.473","modified":"2026-09-30T17:32:07.107","status":"Deferred","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.","cvss_v4":{"vector":"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","score":6.3},"cvss_v3":null,"cwes":["CWE-400"],"references":["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/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c","https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:56:02.509636177+00:00"},"epss":{"cve":"CVE-2026-59980","score":0.00302,"percentile":0.22667,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-8v8h-hg4w-mvq2","url":"https://osv.dev/vulnerability/GHSA-8v8h-hg4w-mvq2","summary":"hpack: Unbounded variable integer decoding can cause run-away computation on malformed input","modified":"2026-10-01T17:55:38.238084125Z","packages":[{"ecosystem":"PyPI","name":"hpack","purl":"pkg:pypi/hpack","ranges":["<4.2.0"],"fixed":["4.2.0"]}]},{"id":"PYSEC-2026-4053","url":"https://osv.dev/vulnerability/PYSEC-2026-4053","summary":"hpack: Unbounded variable integer decoding can cause run-away computation on malformed input","modified":"2026-10-01T17:45:03.832893385Z","packages":[{"ecosystem":"PyPI","name":"hpack","purl":"pkg:pypi/hpack","ranges":["<4.2.0"],"fixed":["4.2.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}