CVE-2026-59980CWE-400denial-of-service

CVE-2026-59980

published September 24, 2026

CVSS
6.3
EPSS
0%
Percentile
21.7
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS
6.3 · NONE
CVSS v4.0
6.3 · 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
EPSS
0.00301 · 21.7th percentile
Weakness
CWE-400 · Uncontrolled Resource Consumption
Published
2026-09-24T03:17Z
References (4)
https://cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18a · [email protected]https://docs.rs/http2/0.5.19/src/http2/hpack/decoder.rs.html#403 · [email protected]https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c · [email protected]https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2 · [email protected]
EPSS history
Timeline
  • 25 SEP 03:26Z
    EPSS moved — → 0%
    epss
  • 23 SEP 22:07Z
    hpack: Unbounded variable integer decoding can cause run-away computation on malformed input
    cvelistv5