russh: Unbounded memory allocation in agent protocol server via crafted constraint records

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.3 · CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2026-111061: 0.35% estimated exploitation activity in the next 30 days; percentile 28.33 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary russhkeys::agent::server::addkey (russh/src/keys/agent/server.rs:271-319) spawns a dedicated tokio task for every 5-byte SSHAGENTCONSTRAINLIFETIME 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…

Published by the source

19 Oct 2026, 17:06 UTC

Last modified by the source

19 Oct 2026, 17:15 UTC

Source last checked

26 Oct 2026, 15:43 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-4wc5-f2rc-q74m

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-4wc5-f2rc-q74m

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# Patch Next advisory brief: CVE-2026-111061

Advisory: russh: Unbounded memory allocation in agent protocol server via crafted constraint records
IDs: CVE-2026-111061, GHSA-4wc5-f2rc-q74m
Record: https://patchnext.com/advisories/cve-2026-111061 (revision 2, source checked 26 Oct 2026, 15:43 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: russh 0.64.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io russh: affected <= 0.64.0; fixed in 0.64.1

## Suggested inspection (read-only)
- crates.io russh: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on russh.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-4wc5-f2rc-q74m (OSV record GHSA-4wc5-f2rc-q74m lists affected ranges: crates.io russh >=0 <0.64.1 (fixed))
- Verified: https://github.com/advisories/GHSA-4wc5-f2rc-q74m (GitHub-reviewed advisory GHSA-4wc5-f2rc-q74m lists affected ranges: crates.io russh >=0 <=0.64.0)

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