vulnerability / NVI-00012142 / Revision 3
russh: Unbounded memory allocation in agent protocol server via crafted constraint records
GitHub lists this reviewed advisory for russh. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
4.3 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
4.3 MEDIUM (3.1)
security-advisories@github.com severity; no combined Null risk score.
0.347%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.28302. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
russh
source listed<= 0.64.0
### Summary `russh_keys::agent::server::add_key` (`russh/src/keys/agent/server.rs:271-319`) spawns a dedicated tokio task for every 5-byte `SSH_AGENT_CONSTRAIN_LIFETIME` record attached to an added key, each cloning the key blob and sleeping for the declared lifetime (up to ~136 years). The loop has no per-request task budget, and spawned tasks are not rolled back when the overall request fails. Repeating one constrained add-key message over an agent connection converts wire bytes into resident tasks and heap at roughly 141x amplification: in our measurement 10.2 MiB of protocol traffic produced ~2,096,120 live tasks and +1,447,856 KiB RSS, while the same traffic sent as unconstrained add-key requests cost +268 KiB. An attacker reaching the agent socket (a local process, or a remote SSH server the user connects to with agent forwarding, since russh clients accept the `auth-agent@openssh.com` channel by default at `russh/src/client/mod.rs:2686`) can exhaust the agent process's memory and task capacity with a renewable, cheap request stream. Verified on russh HEAD efa9a03 (v0.63.3-10, 2026-10-01). ### Details ```rust // russh/src/keys/agent/server.rs:271-319 (add_key, constraint
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-4wc5-f2rc-q74m ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-111061 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-111061 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Source facts changed; compare the preserved prior revision.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.