CVE-2023-26964 is a high-severity (CVSS 7.5) CWE-770 vulnerability in h2. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for h2 — see the affected versions and patch details below.
h2 vulnerable to denial of service
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-26964.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
h2Real-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
Hyper is an HTTP library for Rust and h2 is an HTTP 2.0 client & server implementation for Rust. An issue was discovered in h2 v0.2.4 when processing header frames. It incorrectly processes the HTTP2 RST_STREAM frames by not always releasing the memory immediately upon receiving the reset frame, leading to stream stacking. As a result, the memory and CPU usage are high which can lead to a Denial of Service (DoS).
This issue affects users only when dealing with http2 connections.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | h2 | all versions | 0.3.17cargo update -p h2 --precise 0.3.17 |
Affected Products
h2hyperhyperhyperResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
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.
Fix
Update h2 to 0.3.17 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-26964 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2023-26964 in your dependencies?
Find it across crates.io, including transitive dependencies.