Description
Russh is a Rust SSH client & server library. Prior to 0.62.4, an unauthenticated SSH client can cause a denial of service by sending SSH_MSG_KEX_ECDH_INIT with a 32-byte all-zero Q_C value. Curve25519Kex::server_dh in russh/src/kex/curve25519.rs accepts the all-zero peer public value and computes an all-zero shared secret, after which compute_exchange_hash calls encode_mpint in russh/src/kex/mod.rs and indexes beyond the end of the input while skipping leading zero bytes. The resulting panic occurs before authentication and terminates the server key-exchange task. This issue is fixed in version 0.62.4.
Published: 2026-08-12
Score: 5.3 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

An unauthenticated SSH client can cause a server to panic during key exchange by sending an all‑zero Curve25519 public value. The rust SSH library processes the malformed input and triggers an out‑of‑bounds read, terminating the key‑exchange task before authentication completes. The result is a denial of service, with the server stopping further connections, but no corruption of data or elevation of privilege.

Affected Systems

The vulnerability affects the russh library developed by Eugeny. All releases older than version 0.62.4 are impacted. Newer releases have applied the fix.

Risk and Exploitability

The CVSS score of 5.3 indicates moderate severity. EPSS data are not available and the issue is not listed in the CISA KEV catalog, suggesting low current exploitation activity. The attack vector is remote and pre‑authentication; an attacker only needs the ability to send a crafted SSH_MSG_KEX_ECDH_INIT packet to exploit the flaw. Exploitation results solely in service disruption rather than code execution or data compromise.

Generated by OpenCVE AI on August 13, 2026 at 02:17 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade the russh library to version 0.62.4 or later, which contains the fix for the all‑zero Curve25519 value check.
  • If an upgrade cannot be performed immediately, modify the source to validate incoming peer public key values and reject all‑zero Q_C values prior to shared‑secret computation.
  • Restrict inbound SSH connections to trusted IP addresses via firewall or access control rules to limit the impact until the library can be updated.

Generated by OpenCVE AI on August 13, 2026 at 02:17 UTC.

Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-5xvq-cp9x-6p6r Russh: Pre-auth remote panic via all-zero Curve25519 peer public value (encode_mpint OOB)
History

Sat, 15 Aug 2026 01:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Wed, 12 Aug 2026 23:15:00 +0000

Type Values Removed Values Added
First Time appeared Eugeny
Eugeny russh
Vendors & Products Eugeny
Eugeny russh

Wed, 12 Aug 2026 21:00:00 +0000

Type Values Removed Values Added
Description Russh is a Rust SSH client & server library. Prior to 0.62.4, an unauthenticated SSH client can cause a denial of service by sending SSH_MSG_KEX_ECDH_INIT with a 32-byte all-zero Q_C value. Curve25519Kex::server_dh in russh/src/kex/curve25519.rs accepts the all-zero peer public value and computes an all-zero shared secret, after which compute_exchange_hash calls encode_mpint in russh/src/kex/mod.rs and indexes beyond the end of the input while skipping leading zero bytes. The resulting panic occurs before authentication and terminates the server key-exchange task. This issue is fixed in version 0.62.4.
Title Russh: Pre-auth remote panic via all-zero Curve25519 peer public value (encode_mpint OOB)
Weaknesses CWE-754
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

Subscriptions

Eugeny Russh
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-08-13T17:53:22.532Z

Reserved: 2026-08-12T14:32:11.796Z

Link: CVE-2026-73430

cve-icon Vulnrichment

Updated: 2026-08-13T17:49:21.163Z

cve-icon NVD

Status : Received

Published: 2026-08-12T21:17:41.883

Modified: 2026-08-13T18:18:17.593

Link: CVE-2026-73430

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-13T02:30:12Z

Weaknesses
  • CWE-754

    Improper Check for Unusual or Exceptional Conditions