russh: negotiating a MAC-requiring block cipher (CTR/CBC) with mac=none causes a slice-index-out-of-range panic

Exploitation

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

CVSS

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

EPSS

• CVE-2026-102822: 0.33% estimated exploitation activity in the next 30 days; percentile 25.80 (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 SshBlockCipher implementations (AES-CBC, AES-CTR, 3DES-CBC, etc.) report needsmac() == true, meaning they are documented/intended to always be paired with a separate integrity MAC. However, key-exchange negotiation only checks needsmac() inside the fallback branch of MAC algorithm selection (used when no common MAC algorithm exists). If both peers' preferred MAC lists simply contain none and it is successfully negotiated through the normal selection path, nothing rejects pairing none with a cipher that requires a MAC. Once negotiated, a single crafted packet from either peer causes cipher::read() to shrink an already-allocated buffer below the number of bytes it is about to index, causing a Rust slice-index-out-of-range panic and killing that connection's task. Details In russh/src/cipher/mod.rs, read() for a block cipher: 1. Reads packetlengthtoreadforblocklength() bytes up front (16 bytes for any SshBlockCipher) into buffer.buffer. 2. Decrypts the first block to recover the…

Published by the source

30 Sep 2026, 23:27 UTC

Last modified by the source

30 Sep 2026, 23:45 UTC

Source last checked

26 Oct 2026, 15:43 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-p8qx-h547-fjw9

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-p8qx-h547-fjw9

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# Patch Next advisory brief: CVE-2026-102822

Advisory: russh: negotiating a MAC-requiring block cipher (CTR/CBC) with mac=none causes a slice-index-out-of-range panic
IDs: CVE-2026-102822, GHSA-p8qx-h547-fjw9
Record: https://patchnext.com/advisories/cve-2026-102822 (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: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: russh 0.63.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io russh: affected <= 0.63.0; fixed in 0.63.1

## 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-p8qx-h547-fjw9 (OSV record GHSA-p8qx-h547-fjw9 lists affected ranges: crates.io russh >=0 <0.63.1 (fixed))
- Verified: https://github.com/advisories/GHSA-p8qx-h547-fjw9 (GitHub-reviewed advisory GHSA-p8qx-h547-fjw9 lists affected ranges: crates.io russh >=0 <=0.63.0)

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