huntrule

Linux sshd Logs: Flag Failed Curve25519 Key Generation Indicative of libSSH CVE-2023-2283 Attempts

Alerts on sshd log entries with 'Failed to generate curve25519 keys' that may indicate CVE-2023-2283 libssh bypass attempts.

FreeReviewedSigma · Medium · v5
Product
linux
Service
sshd
Author
Florian Roth (Nextron Systems) (SigmaHQ), DRL 1.1
Published
2023-06-09
Updated
2026-07-31
AnalysisDetection

ATT&CK techniques

Initial Access

  1. Recon

  2. Resource Dev

  3. Initial Access

  4. Execution

  5. Persistence

  6. Priv Esc

  7. Defense Evasion

  8. Cred Access

  9. Discovery

  10. Lateral Movement

  11. Collection

  12. C2

  13. Exfiltration

  14. Impact

What it detects

This rule flags SSH daemon log entries containing “Failed to generate curve25519 keys,” which can indicate a libSSH authentication-bypass attempt tied to CVE-2023-2283. Attackers may trigger this specific error condition during exploitation, and successful exploitation is not required for the event to appear. It relies on Linux sshd service telemetry that records the failure message in its logs.

Reporting behind it

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Linux sshd Logs: Flag Failed Curve25519 Key Generation Indicative of libSSH CVE-2023-2283 Attempts
Pivot detection · T1190 · 9 related

Changelog

v5
  1. v5
    Candidate ingested via manual entry.2026-07-31
  2. v4
    Candidate ingested via manual entry.2026-07-31
  3. v3
    Candidate ingested via manual entry.2026-07-31
  4. v2
    Candidate ingested via manual entry.2026-07-31
  5. v1
    No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.