Russh: SSH identification parsing accepted non-canonical client banners and did not bound pre-banner input

Exploitation

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

CVSS

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

EPSS

• CVE-2026-48108: 0.28% estimated exploitation activity in the next 30 days; percentile 20.16 (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 russh did not enforce the SSH identification-string rules as deliberately as OpenSSH. In particular, the server-side identification reader used the same permissive path as the client, allowing pre-banner lines from clients, and the reader did not enforce a bounded number of pre-banner lines. For a library server built on russh, this could allow a remote peer to hold connection setup resources in the cleartext pre-authentication phase with malformed identification input that should have been rejected early. Details RFC 4253 section 4.2 defines the SSH protocol version exchange. The identification string is a single line terminated by CR LF, must fit within 255 characters including CR LF, and clients should not send pre-banner lines before their SSH identification string. Before the fix, russh's identification reader lived in: - russh/src/sshread.rs - russh/src/server/mod.rs The same readsshid() behavior was used for both client and server contexts. That allowed server-side…

Published by the source

11 Jun 2026, 20:29 UTC

Last modified by the source

11 Jun 2026, 20:29 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-76r6-x97p-67vr

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# Patch Next advisory brief: CVE-2026-48108

Advisory: Russh: SSH identification parsing accepted non-canonical client banners and did not bound pre-banner input
IDs: CVE-2026-48108, GHSA-76r6-x97p-67vr
Record: https://patchnext.com/advisories/cve-2026-48108 (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 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: russh 0.61.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io russh: affected >= 0.34.0-beta.1, < 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-76r6-x97p-67vr (GitHub-reviewed advisory GHSA-76r6-x97p-67vr lists affected ranges: crates.io russh >=0.34.0-beta.1 <0.61.0)

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