CVE-2026-60001: OpenSSH Authentication Delay Bypass (CVSS 6.5)

Technical summary

The sshd daemon in OpenSSH prior to version 10.4 does not consistently apply the minimum authentication delay (typically controlled via the LoginGraceTime or related parameters) when processing failed authentication attempts. This represents a violation of CWE-770 (Allocation of Resources Without Limits or Throttling), allowing rapid-fire authentication attempts without the intended rate-limiting protection. An attacker on the network can exploit this by sending multiple authentication requests in quick succession, bypassing the temporal friction designed to mitigate brute-force attacks.

Business impact

Organizations running vulnerable OpenSSH versions face elevated risk of credential compromise through accelerated brute-force attacks against SSH. This is particularly concerning for systems exposed to untrusted networks or those protecting high-value accounts (service accounts, administrative users). Successful compromise can lead to unauthorized server access, lateral movement, data exfiltration, or establishment of persistent backdoors. The window of exposure depends on deployment scope—organizations with many externally facing SSH servers should prioritize remediation.

Affected systems

OpenSSH versions before 10.4 are affected. This includes all distributions and systems running older OpenSSH releases (9.x, 8.x, and earlier). Verify your current version by running 'ssh -V' on affected systems. Common vulnerable platforms include Linux distributions (Ubuntu, CentOS, Debian, etc.), BSD systems, macOS, and other Unix-like operating systems relying on the standard OpenSSH package.

Exploitability

Exploitation requires only network access to the SSH service (default port 22 or configured alternative). No authentication is required to launch the attack, and the vulnerability does not require user interaction. An attacker can automate rapid login attempts using standard SSH tools. The attack surface is broad: any system with SSH enabled and exposed (directly or via VPN) can be targeted. However, successful compromise still depends on weak credentials or key reuse; systems with strong, unique passwords and key-based authentication remain more resilient.

Remediation

Upgrade OpenSSH to version 10.4 or later on all affected systems. This is the primary remediation. As an interim mitigation, organizations can implement rate-limiting at the network perimeter (using firewall rules or WAF policies to throttle SSH connection attempts) or disable password authentication in favor of key-based authentication only, which is significantly harder to brute-force.

Patch guidance

Obtain OpenSSH 10.4 or later from the official OpenSSH project website or through your distribution's package manager. Verify the release notes and checksums from openbsd.org before installation. Test the upgrade in a non-production environment first, as sshd restarts may briefly interrupt connectivity. Most distributions allow in-place upgrades with minimal disruption; plan the update during a maintenance window if possible. After patching, restart the sshd service and verify connectivity from multiple clients.

Detection guidance

Review SSH logs (typically /var/log/auth.log or /var/log/secure) for patterns of rapid, failed authentication attempts from single or multiple source IPs, particularly targeting service accounts or administrative users. Configure alerts on your centralized logging system for repeated failed SSH login attempts within short time windows. Monitor the sshd process behavior for unexpected CPU or network load that might indicate brute-force activity. Intrusion detection systems should alert on high-frequency SSH protocol activity from single sources.

Why prioritize this

Although rated MEDIUM severity (CVSS 6.5), this vulnerability directly enables brute-force attacks—a common, practical attack vector. Organizations with weak or shared credentials, or those in high-threat environments, should treat this as higher priority. Systems running SSH on the public internet or accessible to untrusted networks warrant faster patching than internal-only systems. The ease of exploitation and direct threat to credential security justifies prioritization within the MEDIUM-severity tier.

Risk score, explained

CVSS 3.1 score of 6.5 reflects a network-accessible, low-complexity attack with no privilege requirement and no user interaction, but with limited impact (integrity and availability affected, not confidentiality). The scoring assumes default SSH configurations; organizations with additional compensating controls (rate-limiting, key-only auth, network segmentation) experience reduced real-world risk. The 'I:L' (Integrity Low) and 'A:L' (Availability Low) components account for the indirect nature of the impact: the vulnerability enables attacks but does not directly compromise data or services.

Frequently asked questions