regreSSHion: OpenSSH Pre-Authentication Remote Code Execution

Signal race condition vulnerability in OpenSSH's server (sshd) on glibc-based Linux systems, allowing unauthenticated remote code execution as root.

EPSS Exploit Probability94.12%

99.2th percentile

Exploit Maturitypoc public

Active Weaponization

Primary VendorsOpenSSH, Ubuntu, Debian, Red Hat, Alpine

1 product(s) impacted

Ransomware CampaignNone documented

Threat intel association

CVSS v3.1 Vector Breakdown

Comprehensive attack metric decomposition according to FIRST specification

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

Attack Vector (AV)NETWORKRemotely exploitable over network

Attack Complexity (AC)HIGHNo specialized access needed

Privileges Required (PR)NONEUnauthenticated exploitation

User Interaction (UI)NONEZero-click / autonomous

Scope (S)UNCHANGEDSecurity authority boundary

Confidentiality (C)HIGHTotal information disclosure

Integrity (I)HIGHTotal compromise of system state

Availability (A)HIGHComplete resource denial

TechOverwatch AI Security Sentinel Analysis

Model: Gemini 2.0 Flash Security Sentinel · Generated: 2026-10-28

Executive Defense Summary

A resurrected regression in OpenSSH (hence regreSSHion) that re-introduced a critical signal-handler race condition from 2006. Enables remote root compromise of internet-exposed Linux systems.

Technical Root Cause Architecture

In OpenSSH 8.5p1, commit b98c080 accidentally removed an `#ifdef DO_LOG_SAFE_IN_SIGHAND` guard around the SIGALRM signal handler in `sigdie()`. Because `syslog()` invokes non-reentrant heap allocators, interrupted malloc operations corrupt the glibc chunk meta-structures, allowing precise heap shaping over hundreds of parallel connections.

Exploitation Scenario & Attack Chain

Exploitation involves winning a split-second race condition during connection timeout on 32-bit and 64-bit architectures by repeatedly flooding the target with parallel connections and manipulating heap alignment until the instruction pointer redirects to shellcode.

Enterprise Blast Radius & Lateral Risk

Direct unauthenticated root access to host operating system, full compromise of virtualization hosts, perimeter firewalls, and cloud bastion nodes.

Remediation & Defense Playbook

Immediate actionable steps for DevOps, SecOps, and Security Architects

1Update OpenSSH packages to version 9.8p1 or vendor backports immediately.

2Workaround if patching is delayed: set `LoginGraceTime 0` in `/etc/ssh/sshd_config` and reload the service. Note: This exposes sshd to denial of service from open connections.

3Implement strict network segmentation: sshd ports (22) must never be open to the public internet; enforce VPN, WireGuard, or Cloudflare Access tunnels.

Detection Guidance & Threat Hunting

Look for high volumes of closed SSH connections with 'Timeout before authentication for [IP]' in auth.log or secure syslog files.

Sigma Detection Rule (SIEM Export)

title: OpenSSH regreSSHion Exploitation Attempt
status: high
logsource:
  product: linux
  service: sshd
detection:
  selection:
    message|contains: 'Timeout before authentication for'
  condition: selection | count() by src_ip > 50

Affected Software & CPE Matrix

Targeted versions, patched releases, and Common Platform Enumerations

Vendor	Product	Affected Versions	Fixed In
OpenBSD	OpenSSH	8.5p1 up to but excluding 9.8p1 (also earlier versions 3.4p1)	OpenSSH 9.8p1

Official Advisories & Authoritative Sources

Qualys Security Advisory: regreSSHion (CVE-2024-6387)https://www.qualys.com/2024/07/01/cve-2024-6387/regresshion.txt

advisory

OpenSSH 9.8 Release Noteshttps://www.openssh.com/txt/release-9.8

patch

AI Agent & Security Automation Hub

TechOverwatch provides native machine-readable endpoints for autonomous agents, Cursor, Claude, ChatGPT, and automated patch scanners.

Agent CLI Command (curl):

curl -s https://www.techoverwatch.in/api/vulnerabilities/CVE-2024-6387/raw

Raw Markdown JSON API