RegreSSHion: Why a Six-Month-Old Vulnerability is Relevant Again
Cybersecurity professionals know that vulnerabilities rarely fade into obscurity just because they’re patched or reported. The release of a public proof of concept (PoC) can breathe new life into old threats. That’s precisely what’s happened with the RegreSSHion vulnerability (CVE-2024-6387), which we covered in detail six months ago here. Now, with a fully functional PoC available, it’s time to revisit why this vulnerability demands attention – and action.
The State of Play: What’s Changed?
On July 1st, 2024, the RegreSSHion vulnerability made some splashes across news outlets – as is often the case with named vulnerabilities. Its combination of wide applicability and potential for remote code execution made it a significant concern, even if the exploit relied on precise timing and probabilistic success.
Fast forward six months, and a PoC has been publicly released and can now be found on github (which we will intentionally not link to). This tool simplifies the process of identifying vulnerable OpenSSH servers and, potentially, exploiting the flaw.
While the exploit still depends on timing a race condition – a challenge for attackers – it’s now within reach of a much larger pool of threat actors. Simply put, the barrier to entry has been lowered, and the risk to unpatched systems has escalated.
What the PoC Tells Us
The PoC script is a lightweight, efficient scanner capable of detecting vulnerable OpenSSH versions. It includes features like rapid scanning across multiple IPs and network ranges, detection of grace time changes to identify mitigations, and identification of patched versions.
Notably, the exploit is confirmed to work on 32-bit OpenSSH servers (of which there are still a considerable number out there, apparently) and targets systems using default settings, such as a LoginGraceTime of 120 seconds. While the time required to execute the exploit remains probabilistic – ranging from hours to days for a successful attack – the PoC eliminates much of the complexity involved in crafting such an attack manually.
The Call to Action: Patch Now, If You Haven’t Already
If your organization hasn’t patched OpenSSH to a version known to mitigate RegreSSHion, now is the time. The existence of a publicly available PoC makes it significantly easier for attackers to probe for weaknesses and execute targeted attacks.
Refer to our original article for a deep dive into the vulnerability and its exploit mechanics. In summary, ensure the following:
- Upgrade OpenSSH to a patched version, specifically one beyond the affected range of 8.5p1 to 9.8p1.
- Reduce exposure of SSH services by restricting access to internal networks or using VPNs.
- Harden configurations, such as reducing LoginGraceTime and enabling other security features like fail2ban.
- Monitor logs for suspicious login attempts or timeout patterns.
Why It’s Critical to Act Quickly
Even though the exploit remains difficult to trigger, a determined attacker can optimize the process for specific targets. Furthermore, widespread internet scans have identified millions of exposed SSH servers, many of which are, still, likely unpatched. This amplifies the importance of proactive mitigation, especially for organizations that may not have prioritized updates when the vulnerability was first disclosed.
Final Thoughts
Cybersecurity is a constant race against time, and vulnerabilities like RegreSSHion are a reminder of why timely patching is non-negotiable. While the vulnerability has existed for months, the newly available PoC has reignited its relevance and increased the risk landscape.
Don’t wait for an attacker to knock on your door. Patch your systems, close unnecessary exposures, and stay ahead of the curve.


