RegreSSHion OpenSSH Bug Check

The Recent OpenSSH Vulnerability (CVE-2023-38408):

Update : July 3, 24 12:46 pm – Exploit code link here. RegreSSHion Ip Scanner tool here.

This vulnerability, discovered in July 2023, affects OpenSSH versions 9.3 and 9.3p1. It’s specifically related to the implementation of RSA keys with SHA-2 signature algorithms. Read on for more on the RegreSSHion OpenSSH Bug Check. Here’s a detailed breakdown:

  1. Nature of the Vulnerability:
    • It’s a regression bug that causes connection failures when using RSA keys with SHA-2 signature algorithms.
    • The bug affects the key exchange process, specifically during the server authentication phase.

The recent discovery of the regreSSHion OpenSSH bug has underscored the critical importance of thorough testing and validation in software development. This particular bug, identified in OpenSSH versions 9.3 and 9.3p1, affects the handling of RSA keys with SHA-2 signature algorithms. As organizations rely heavily on OpenSSH for secure remote access and file transfers, the need for a robust regreSSHion OpenSSH bug check process becomes evident. Ensuring that new updates do not introduce vulnerabilities is crucial for maintaining the integrity and security of systems.

regresshion openssh bug check

A regreSSHion OpenSSH bug check involves systematically testing new versions of OpenSSH against known vulnerabilities and ensuring that previously fixed issues do not reappear. This process typically includes automated testing, manual code reviews, and extensive validation against a variety of configurations and use cases. By implementing a comprehensive regreSSHion OpenSSH bug check, developers can catch potential issues early in the development cycle, reducing the risk of deploying flawed software.

In the case of the recent OpenSSH vulnerability, a regreSSHion OpenSSH bug check could have identified the issue with RSA-SHA2 signature handling before the affected versions were released. This would have allowed the development team to address the problem proactively, avoiding the widespread disruptions caused by authentication failures. Organizations that perform regular regreSSHion OpenSSH bug checks are better equipped to maintain secure and reliable systems, even as they adopt new features and updates.

Qualys, a well-known cybersecurity firm, attempted to write a proof-of-concept (PoC) exploit for the regreSSHion OpenSSH bug. Their efforts underscore the importance of understanding how vulnerabilities can be exploited in real-world scenarios. By developing a PoC, Qualys aimed to demonstrate the potential impact of the regreSSHion OpenSSH bug and provide valuable insights for mitigating the risk. This approach highlights the need for continuous security assessments and the role of regreSSHion OpenSSH bug checks in safeguarding critical infrastructure.

For organizations looking to implement their own regreSSHion OpenSSH bug check, several best practices can be followed. These include maintaining a comprehensive test suite that covers all supported configurations, using automated tools to detect changes in behavior, and conducting regular security audits. Additionally, staying informed about the latest vulnerabilities and patches is essential for keeping systems secure. By prioritizing regreSSHion OpenSSH bug checks, organizations can ensure that their OpenSSH deployments remain resilient against emerging threats.

  1. RSA-SHA2 Signature Algorithms:
    • OpenSSH has been supporting RSA keys with SHA-2 signature algorithms (RSA-SHA2-256/512) since version 7.2.
    • These algorithms were introduced to replace the older SHA-1 based signatures, which are considered less secure.
  2. The Problem:
    • In affected versions, when a client attempts to authenticate using an RSA key with SHA-2 signatures, the server fails to properly process the signature.
    • This results in authentication failures, even with valid keys and correct configurations.
  3. Impact:
    • Users relying on RSA keys with SHA-2 signatures may be unable to connect to servers running the affected OpenSSH versions.
    • This can lead to service disruptions and potential lockouts from systems.
  4. Affected Configurations:
    • The bug primarily affects setups where RSA keys are used with the SHA-2 signature algorithms.
    • It’s particularly problematic because many modern configurations prefer or require SHA-2 signatures for enhanced security.
  5. Root Cause:
    • The issue stems from a change in how OpenSSH handles the RSA-SHA2 signature verification process.
    • Specifically, there was an error in the code that verifies the RSA signature length, causing valid signatures to be rejected.
  6. Workarounds:
    • Temporarily switching to RSA-SHA1 signatures (not recommended for long-term use due to security concerns).
    • Using alternative key types like Ed25519 or ECDSA, if supported by both client and server.
  7. Fix:
    • OpenSSH quickly released version 9.3p2 to address this vulnerability.
    • The fix involves correcting the signature length verification process for RSA-SHA2 signatures.
  8. Broader Context:
    • This vulnerability highlights the challenges in maintaining backward compatibility while implementing newer, more secure cryptographic standards.
    • It also underscores the importance of thorough testing when making changes to critical security components like signature verification.
  9. Lessons Learned:
    • The incident emphasizes the need for robust testing of cryptographic implementations, especially when dealing with different key types and signature algorithms.
    • It also highlights the importance of having fallback mechanisms and quick update processes in place for critical security software.
  10. Detection:
    • Systems affected by this vulnerability would typically show authentication failures in logs when clients attempt to connect using RSA keys with SHA-2 signatures.
    • Network monitoring tools might detect an increase in failed SSH connection attempts.
  11. Mitigation Strategies:
    • Updating to OpenSSH version 9.3p2 or later is the primary mitigation strategy.
    • For systems that can’t be immediately updated, temporarily allowing RSA-SHA1 signatures (with caution) or switching to alternative key types can serve as short-term solutions.

Based on the information provided, here are the key points about Qualys’ attempt to write a proof-of-concept (PoC) exploit for the OpenSSH vulnerability CVE-2024-6387 (dubbed “regreSSHion”):

  1. Qualys discovered the vulnerability and reported it responsibly. They did not publicly release a full PoC exploit to prevent malicious exploitation.
  2. The vulnerability is a signal handler race condition in OpenSSH’s server (sshd) that allows unauthenticated remote code execution as root on glibc-based Linux systems.
  3. Qualys provided technical details on how the vulnerability works, including that it’s a regression of a previously patched vulnerability from 2006 (CVE-2006-5051).
  4. They explained the exploit mechanics involve hitting a very narrow time window, potentially requiring thousands of attempts to succeed.
  5. Qualys shared some indicators of compromise (IoCs) to help organizations detect potential attacks, rather than releasing exploit code.
  6. They demonstrated the vulnerability is exploitable on 32-bit glibc-based Linux systems, and were working on an exploit for 64-bit systems (which is more challenging due to stronger ASLR).
  7. Qualys provided mitigation advice and released detection signatures for their products.

This vulnerability serves as a reminder of the complex interplay between different cryptographic algorithms and the importance of maintaining and updating security protocols. It also highlights the ongoing evolution of SSH implementations as they adapt to changing security requirements and cryptographic standards.

RegreSSHion OpenSSH Bug Check! Based on the information provided, here are some code snippets in Go and Python that could help identify the OpenSSH “RegreSSHion” vulnerability (CVE-2024-6387):

In Go:

Copy Codepackage main

import (

func checkOpenSSHVersion() (string, bool) {
    cmd := exec.Command("ssh", "-V")
    output, err := cmd.CombinedOutput()
    if err != nil {
        fmt.Println("Error executing ssh -V:", err)
        return "", false

    version := strings.TrimSpace(string(output))
    fmt.Println("OpenSSH version:", version)

    // Check if version is vulnerable
    isVulnerable := false
    if strings.Contains(version, "OpenSSH") {
        versionNum := strings.Split(version, "_")[1]
        if versionNum >= "8.5p1" && versionNum < "9.8p1" {
            isVulnerable = true
        } else if versionNum < "4.4p1" {
            isVulnerable = true

    return version, isVulnerable

func main() {
    version, isVulnerable := checkOpenSSHVersion()
    if isVulnerable {
        fmt.Printf("WARNING: OpenSSH version %s is vulnerable to CVE-2024-6387 (RegreSSHion)\n", version)
    } else {
        fmt.Printf("OpenSSH version %s is not vulnerable to CVE-2024-6387 (RegreSSHion)\n", version)

In Python:

Copy Codeimport subprocess
import re

def check_openssh_version():
        output = subprocess.check_output(["ssh", "-V"], stderr=subprocess.STDOUT).decode('utf-8').strip()
        print("OpenSSH version:", output)

        # Extract version number
        match ='OpenSSH_(\d+\.\d+p\d+)', output)
        if match:
            version =
            # Check if version is vulnerable
            if version >= "8.5p1" and version < "9.8p1":
                return output, True
            elif version < "4.4p1":
                return output, True
        return output, False
    except subprocess.CalledProcessError as e:
        print("Error executing ssh -V:", e)
        return "", False

def main():
    version, is_vulnerable = check_openssh_version()
    if is_vulnerable:
        print(f"WARNING: OpenSSH version {version} is vulnerable to CVE-2024-6387 (RegreSSHion)")
        print(f"OpenSSH version {version} is not vulnerable to CVE-2024-6387 (RegreSSHion)")

if __name__ == "__main__":

Both scripts do the following:

  1. Execute the ssh -V command to get the OpenSSH version.
  2. Parse the version string to extract the version number.
  3. Check if the version falls within the vulnerable range (8.5p1 to 9.8p1, or earlier than 4.4p1).
  4. Print a warning if the version is vulnerable.

Note that this is a basic check and doesn’t account for patched versions or specific system configurations. For a comprehensive security assessment, it’s recommended to use professional vulnerability scanning tools or consult with cybersecurity experts.

Now here’s a script that checks for the vuln and then searches for more of it’s instances on!!

a script that scans for this vulnerability, first by checking the port and then by using Shodan for additional information.

Here’s a Python script that does this:

Copy Codeimport socket
import paramiko
import shodan

def check_openssh_version(host, port=22):
        sock = socket.create_connection((host, port), timeout=5)
        transport = paramiko.Transport(sock)
        server_version = transport.remote_version
        return server_version
    except Exception as e:
        print(f"Error connecting to {host}:{port}: {str(e)}")
        return None

def is_vulnerable(version):
    return version in ["SSH-2.0-OpenSSH_9.3", "SSH-2.0-OpenSSH_9.3p1"]

def check_shodan(api_key, ip):
    api = shodan.Shodan(api_key)
        results =
        for item in results['data']:
            if item['port'] == 22:
                return item.get('version', 'Unknown')
    except Exception as e:
        print(f"Error querying Shodan: {str(e)}")
    return None

def main():
    host = input("Enter the host to check: ")
    port = int(input("Enter the port (default 22): ") or 22)
    shodan_api_key = input("Enter your Shodan API key (press Enter to skip Shodan check): ")

    version = check_openssh_version(host, port)
    if version:
        print(f"OpenSSH version: {version}")
        if is_vulnerable(version):
            print("This version is potentially vulnerable to the regression bug (CVE-2023-38408)")
            print("This version is not known to be vulnerable to the regression bug")
    if shodan_api_key:
        shodan_version = check_shodan(shodan_api_key, host)
        if shodan_version:
            print(f"Shodan reports OpenSSH version: {shodan_version}")
            if is_vulnerable(shodan_version):
                print("This version is potentially vulnerable to the regression bug (CVE-2023-38408)")
                print("This version is not known to be vulnerable to the regression bug")

if __name__ == "__main__":

To use this script:

  1. Install the required libraries: pip install paramiko shodan
  2. Run the script: python
  3. Enter the host, port (optional), and Shodan API key (optional) when prompted.

This script does the following:

  1. It first attempts to connect to the specified host and port to retrieve the OpenSSH version.
  2. It checks if the retrieved version matches the known vulnerable versions (9.3 and 9.3p1).
  3. If a Shodan API key is provided, it also queries Shodan for additional information about the host’s SSH service.
  4. It reports whether the host is potentially vulnerable based on both the direct check and the Shodan information.

Please note that this script provides a basic check and may not catch all instances of the RegrSSHion vulnerability. It’s always recommended to perform thorough security audits and keep systems updated with the latest security patches. That’s how you can RegreSSHion OpenSSH Bug Check!

UPDATE: Check out C code exploit here :


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