CVE-2026-59980 — hpack: Unbounded variable integer decoding can cause run-away computation on malformed input
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) ru…
Published: 2026-09-23 · CVSS: 6.3 · CVSS 4.0
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.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7