russh's SSH agent server is susceptible to unbound allocations via repeated SSH_AGENT_CONSTRAIN_CONFIRM messages

Exploitation

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

CVSS

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

EPSS

• CVE-2026-116696: 0.11% estimated exploitation activity in the next 30 days; percentile 1.26 (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 All evidence, reproduction steps, and scripts in the report were verified against a real running instance. Nothing is fabricated or synthetic; every verdict is backed by captured output from an actual deployment. The SSH agent server that ships with russh (`russh::keys::agent::server::serve`) parses client key-addition requests and, for each `SSH_AGENT_CONSTRAIN_CONFIRM` (0x02) record it finds, pushes one `Constraint::Confirm` value into a per-key vector inside an unbounded loop, then stores the resulting pair permanently in its keystore (`russh/src/keys/agent/server.rs:296-303`). Neither the constraint vector nor the keystore has a size or count limit: the only boundary is the 256 KiB agent frame cap, and every 1-byte record a client sends becomes a 56-byte enum retained for the life of the process. Any process that can connect to the agent socket - the same trust model the project itself established when fixing a prior advisory about this same request handler - can…

Published by the source

30 Oct 2026, 22:58 UTC

Last modified by the source

30 Oct 2026, 23:15 UTC

Source last checked

31 Oct 2026, 06:45 UTC

1. Revision 2 · amended · 31 Oct 2026

   Amended from osv record GHSA-9wfm-jcj8-jfv9

2. Revision 1 · created · 30 Oct 2026

   Published from ghsa record GHSA-9wfm-jcj8-jfv9

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# Patch Next advisory brief: CVE-2026-116696

Advisory: russh's SSH agent server is susceptible to unbound allocations via repeated SSH_AGENT_CONSTRAIN_CONFIRM messages
IDs: CVE-2026-116696, GHSA-9wfm-jcj8-jfv9
Record: https://patchnext.com/advisories/cve-2026-116696 (revision 2, source checked 31 Oct 2026, 06:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: russh 0.65.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io russh: affected < 0.65.0; fixed in 0.65.0

## 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://github.com/advisories/GHSA-9wfm-jcj8-jfv9 (GitHub-reviewed advisory GHSA-9wfm-jcj8-jfv9 lists affected ranges: crates.io russh >=0 <0.65.0)
- Verified: https://osv.dev/vulnerability/GHSA-9wfm-jcj8-jfv9 (OSV record GHSA-9wfm-jcj8-jfv9 lists affected ranges: crates.io russh >=0 <0.65.0 (fixed))

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