GHSA-h5rc-j5f5-3gcm is a medium-severity (CVSS 6.5) CWE-190 vulnerability in russh. A fix is available for russh — see the affected versions and patch details below.
russh is missing overflow checks during channel windows adjust
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.
Exploitation and automatability from CISA’s SSVC triage for GHSA-h5rc-j5f5-3gcm.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-h5rc-j5f5-3gcm plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
russhReal-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
Summary
The channel window adjust message of the SSH protocol is used to track the free space in the receive buffer of the other side of a channel. The current implementation takes the value from the message and adds it to an internal state value. This can result in a integer overflow. If the Rust code is compiled with overflow checks, it will panic. A malicious client can crash a server.
Details
According https://datatracker.ietf.org/doc/html/rfc4254#section-5.2, The value must not overflow. The incorrect handling is done in server/encrypted.rs and client/encrypted.rs in the handling of CHANNEL_WINDOW_ADJUST.
let amount = map_err!(u32::decode(&mut r))?;
...
channel.recipient_window_size += amount;
It could be replaced with something like
if let Some(ref mut channel) = enc.channels.get_mut(&channel_num) {
// rfc 4254: The window MUST NOT be increased above 2^32 - 1 bytes.
new_size = channel.recipient_window_size.saturating_add(amount);
channel.recipient_window_size = new_size;
}
...
PoC
A customized client code would be required to send a message with a big value like u32_max. Not done yet.
Impact
This problem seems only critical to a server. One user can crash the server, which might take down the service. A malicious server could also crash a single client, but this seems not very critical.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | russh | all versions | 0.54.1cargo update -p russh --precise 0.54.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for russh, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update russh to 0.54.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-h5rc-j5f5-3gcm is resolved across your whole dependency graph.
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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-h5rc-j5f5-3gcm can be triaged on real exposure rather than presence alone.
Tailored to GHSA-h5rc-j5f5-3gcm. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-h5rc-j5f5-3gcm in your dependencies?
O3 Security finds GHSA-h5rc-j5f5-3gcm across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.