hpack: Unbounded variable integer decoding can cause run-away computation on malformed input
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- Present
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · Low
- Fix status
- Partial Red Hat: 5 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-400.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| python-hyper | hpack | before 4.2.0 | 4.2.0 | Patch available | CNA |
| — | hpack (PyPI) | before 4.2.0 | 4.2.0 | Patch available | GHSA-8v8h-hg4w-mvq2 |
- hpack Vendorpython-hyper Affected before 4.2.0 Fixed in 4.2.0 Patch available CNA
- hpack (PyPI) Vendor— Affected before 4.2.0 Fixed in 4.2.0 Patch available GHSA-8v8h-hg4w-mvq2
Remediation
- Fix · CNA hpack (python-hyper) Fixed in 4.2.0
- Fix · GHSA-8v8h-hg4w-mvq2 hpack (PyPI) Fixed in 4.2.0 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Migration Toolkit for Containers | Affected | No fix yet: Fix deferred |
| Red Hat Ansible Automation Platform 2 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift AI (RHOAI) | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 17.1 | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 18.0 | Affected | No fix yet: Fix deferred |
Not affected: 1 product
- Red Hat Hardened Images
Timeline
- 2026-10-02 Threatist record created from CVE-2026-59980
- 2026-10-03 Alias added: GHSA-8v8h-hg4w-mvq2
References
Other 6
- https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2
- https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c
- 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
- https://github.com/python-hyper/hpack/releases/tag/v4.2.0
More python-hyper vulnerabilities
- TI-2026-79288 Out-of-bounds write in Google Brotli decoder KEVCVSS 4.0CRITICAL 9.2
- TI-2025-28443 h11 accepts some malformed Chunked-Encoding bodies CVSS 3.1CRITICAL 9.1
- TI-2025-35687 h2 allows HTTP Request Smuggling due to illegal characters in headers CVSS 4.0MEDIUM 6.9
- TI-2026-50126 h2: Duplicate Host header could facilitate request smuggling CVSS 3.1MEDIUM 5.3
Sources
- CVE-2026-59980 · CVE Program
- CVE-2026-59980 · NVD
- FIRST EPSS
- GHSA-8v8h-hg4w-mvq2 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-59980 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences