Russh: Unchecked keyboard-interactive prompt count in client auth path

Exploitation

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

CVSS

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

EPSS

• CVE-2026-48107: 0.23% estimated exploitation activity in the next 30 days; percentile 14.13 (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 In the russh client keyboard-interactive authentication path, a malicious SSH server could send a USERAUTHINFOREQUEST with an attacker-controlled prompt count, and the client would use that raw count directly in Vec::withcapacity(...) before validating that enough prompt data was actually present in the packet. This is a client-side denial-of-service / resource-exhaustion issue on the keyboard-interactive auth path. Details The vulnerable code path is in: - russh/src/client/encrypted.rs When the client is in CurrentRequest::KeyboardInteractive state and receives SSHMSGUSERAUTHINFOREQUEST, it parses: 1. name 2. instructions 3. language tag 4. nprompts Before the fix, the code then did: That means a malicious server could advertise an enormous nprompts value even if the packet contained no prompt bodies at all. The fix rejects inconsistent prompt counts before allocating: Each prompt needs at least 4 bytes of string length plus 1 byte of echo flag, so remaininglen() / 5 is a…

Published by the source

11 Jun 2026, 20:28 UTC

Last modified by the source

11 Jun 2026, 20:28 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-g9g7-5cgw-6v28

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# Patch Next advisory brief: CVE-2026-48107

Advisory: Russh: Unchecked keyboard-interactive prompt count in client auth path
IDs: CVE-2026-48107, GHSA-g9g7-5cgw-6v28
Record: https://patchnext.com/advisories/cve-2026-48107 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: russh 0.61.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io russh: affected >= 0.37.0, < 0.61.0; fixed in 0.61.0

## 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-g9g7-5cgw-6v28 (GitHub-reviewed advisory GHSA-g9g7-5cgw-6v28 lists affected ranges: crates.io russh >=0.37.0 <0.61.0)

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