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

Analysis Detection

ATT&CK techniques

Initial Access

Recon
Resource Dev
Initial Access
- T1190Exploit Public-Facing Application
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
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
Candidate ingested via manual entry.2026-07-31
v4
Candidate ingested via manual entry.2026-07-31
v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
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.

linux-sshd-flag-failed-curve25519-key-generation-suggesting-libssh-authenticatio-8b244735

title: "Linux sshd Logs: Flag Failed Curve25519 Key Generation Indicative of libSSH CVE-2023-2283 Attempts"
id: f6f25051-59e3-4b0e-95f8-4ed928dec009
status: test
description: 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.
references:
  - https://twitter.com/kevin_backhouse/status/1666459308941357056?s=20
  - https://git.libssh.org/projects/libssh.git/tree/src/curve25519.c#n420
  - https://nvd.nist.gov/vuln/detail/CVE-2023-2283
  - https://www.blumira.com/cve-2023-2283/
  - https://github.com/github/securitylab/tree/1786eaae7f90d87ce633c46bbaa0691d2f9bf449/SecurityExploits/libssh/pubkey-auth-bypass-CVE-2023-2283
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2023/Exploits/CVE-2023-2283/lnx_sshd_exploit_cve_2023_2283_libssh_authentication_bypass.yml
author: Florian Roth (Nextron Systems), Huntrule Team
date: 2023-06-09
tags:
  - attack.initial-access
  - attack.t1190
  - cve.2023-2283
  - detection.emerging-threats
logsource:
  product: linux
  service: sshd
detection:
  keywords:
    - Failed to generate curve25519 keys
  condition: keywords
falsepositives:
  - Errors with the initialization or generation of the X25519 elliptic curve keys may generate the same error message
level: medium
license: DRL-1.1
related:
  - id: 8b244735-5833-4517-a45b-28d8c63924c0
    type: derived

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