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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| python-hyper | hpack | < 4.2.0 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | python-hpack | No fix yet | — |
| Debian 13 | python-hpack | No fix yet | — |
| Debian 12 | python-hpack | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | python-hpack | No fix yet | — |
| Ubuntu 26.04 LTS | python-hpack | No fix yet | — |
| Ubuntu 24.04 LTS | python-hpack | No fix yet | — |
| Ubuntu 22.04 LTS | python-hpack | No fix yet | — |
| Ubuntu 20.04 LTS | python-hpack | No fix yet | — |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 18.04 LTS | python-hpack | No fix yet | — |
| Ubuntu 16.04 LTS | python-hpack | No fix yet | — |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | python-hpack | 3.0.0-150200.3.5.1 | SUSE-SU-2026:4593-1 |
| SLES 3 | python-hpack | 4.0.0-150400.8.6.1 | SUSE-SU-2026:4832-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | python-hpack | 4.1.0-160000.3.1 | SUSE-SU-2026:24216-1 |
| SLES 16.0 | python-hpack | 4.1.0-160000.3.1 | SUSE-SU-2026:24216-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | python-hpack | 4.2.0-1.1 | openSUSE-SU-2026:11556-1 |
| openSUSE Leap 16.0 | python-hpack | 4.1.0-160000.3.1 | openSUSE-SU-2026:22070-1 |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | python3-hpack | 4.0.0-2.amzn2023.0.3 | ALAS2023-2026-3159 |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| PyPI | hpack | < 4.2.0 | 4.2.0 | GHSA-8v8h-hg4w-mvq2 |
Advisories 6
- SUSE-SU-2026:4832-1 Security update for python-hpack SUSE / openSUSE Security Updates · Oct 22, 2026
- SUSE-SU-2026:24216-1 Security update for python-hpack SUSE / openSUSE Security Updates · Oct 21, 2026
- openSUSE-SU-2026:22070-1 Security update for python-hpack SUSE / openSUSE Security Updates · Oct 19, 2026
- ALAS2023-2026-3159 Important: python-hpack security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Oct 12, 2026
- SUSE-SU-2026:4593-1 Security update for python-hpack SUSE / openSUSE Security Updates · Oct 9, 2026
- openSUSE-SU-2026:11556-1 python313-hpack-4.2.0-1.1 on GA media SUSE / openSUSE Security Updates · Aug 21, 2026
References
- 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