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MEDIUM severity

h2 servers vulnerable to degradation of service with CONTINUATION FloodGHSA-q6cp-qfwq-4gcv

MEDIUM

GHSA-q6cp-qfwq-4gcv is a medium-severity (CVSS 5.3) vulnerability in h2. A fix is available for h2 — see the affected versions and patch details below.

Also known asRUSTSEC-2024-0332
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Sep 10, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

2 pkgs affected
🦀h2🦀h2

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

Description

An attacker can send a flood of CONTINUATION frames, causing h2 to process them indefinitely. This results in an increase in CPU usage.

Tokio task budget helps prevent this from a complete denial-of-service, as the server can still respond to legitimate requests, albeit with increased latency.

More details at https://seanmonstar.com/blog/hyper-http2-continuation-flood/.

Patches available for 0.4.x and 0.3.x versions.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
🦀crates.ioh2all versions0.3.26cargo update -p h2 --precise 0.3.26
🦀crates.ioh2≥ 0.4.0&&< 0.4.40.4.4cargo update -p h2 --precise 0.4.4

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for h2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update h2 to 0.3.26 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-q6cp-qfwq-4gcv is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

An attacker can send a flood of CONTINUATION frames, causing `h2` to process them indefinitely. This results in an increase in CPU usage. Tokio task budget helps prevent this from a complete denial-of-service, as the server can still respond to legitimate requests, albeit with increased latency. More details at https://seanmonstar.com/blog/hyper-http2-continuation-flood/. Patches available for 0.4.x and 0.3.x versions.
O3 Security · Impact-Aware SCA

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h2 servers vulnerable to degradation of service with…