A new critical vulnerability, identified as CVE-2024-6387, has been discovered in OpenSSH. This flaw involves a signal handler race condition that can potentially be exploited by attackers to gain unauthorized access or execute arbitrary code.
OpenSSH: An Overview
OpenSSH, or Open Secure Shell, is a suite of secure networking utilities based on the Secure Shell (SSH) protocol, which provides a secure channel over an unsecured network. It is widely used for remote login, command execution, file transfer, and tunneling services, ensuring encrypted communications between clients and servers.
Key Features of OpenSSH
- Remote Login: Securely log in to remote systems.
- Encrypted Traffic: All traffic between client and server is encrypted, preventing eavesdropping and connection hijacking.
- Data Integrity: Ensures data integrity and confidentiality during transmission.
- Forwarding: Supports TCP/IP and X11 forwarding, allowing secure forwarding of ports and display sessions.
Vulnerability Details
The vulnerability is rooted in the way OpenSSH’s sshd daemon handles certain signals. Specifically, a race condition occurs in the signal handling code that can be triggered under certain conditions. This race condition can lead to memory corruption, allowing an attacker to manipulate memory allocations and potentially execute arbitrary code.
The exploit scenario involves carefully timed interactions with the sshd process, leveraging the signal handling code to create a state where the memory allocation functions (malloc, free) can be manipulated. This manipulation can result in the execution of malicious code or unauthorized access.
The vulnerability CVE-2024-6387, also known as regreSSHion, has exposed a significant number of OpenSSH server instances to potential exploitation. Here are the key findings related to this vulnerability:
- Widespread Exposure: It is estimated that over 14 million OpenSSH server instances are potentially vulnerable and exposed to the internet. These instances are susceptible to remote unauthenticated code execution (RCE), which could allow attackers to gain full control over the affected systems.
- Severity: The vulnerability can be exploited to achieve RCE, particularly affecting systems running glibc-based Linux versions. This makes it a critical security concern for organizations relying on OpenSSH for secure remote communications.
- Historical Context: The flaw has been named regreSSHion because it is a regression of an older vulnerability (CVE-2006-5051) that was previously patched. This highlights the importance of ongoing vigilance and patch management in software security.
Technical Analysis
The detailed technical breakdown provided by Qualys highlights the steps attackers can take to exploit this vulnerability:
- Heap Manipulation: Attackers can free a specific chunk of memory in a non-main arena, redirecting the pointer to OpenSSH’s Global Offset Table (GOT).
- Code Overwrite: By overwriting the entry for
_exit()in the GOT with the address of shellcode, attackers can gain control of the execution flow. - Timing Strategy: The exploitation relies on precise timing to interrupt memory operations, creating a situation where uninitialized memory fields can be controlled by the attacker.
Affected OpenSSH Versions for CVE-2024-6387
The critical vulnerability CVE-2024-6387 impacts various versions of OpenSSH, primarily those released between versions 8.5p1 and 9.7p1. This vulnerability, a signal handler race condition in OpenSSH’s server (sshd), allows for potential remote unauthenticated code execution.
- Vulnerable Versions: OpenSSH versions from 8.5p1 up to 9.7p1.
- Older Versions: Versions earlier than 4.4p1 are also vulnerable unless patched for CVE-2006-5051 and CVE-2008-4109.
- Recent Vulnerability: The race condition in OpenSSH’s
sshdhas made numerous systems susceptible to potential attacks.
Potential Impact of regreSSHion (CVE-2024-6387)
The vulnerability known as “regreSSHion,” identified as CVE-2024-6387, poses significant risks to systems running affected versions of OpenSSH. Here are the potential impacts:
1. Remote Code Execution (RCE)
- Nature: The most critical impact of CVE-2024-6387 is the possibility of remote code execution.
- Consequence: Attackers can execute arbitrary code on the affected systems, potentially gaining full control over the server. This can lead to unauthorized access, data breaches, and further exploitation.
2. Privilege Escalation
- Nature: The vulnerability may allow attackers to escalate their privileges on the compromised system.
- Consequence: An attacker with limited access could exploit this vulnerability to gain root or administrative privileges, significantly increasing the potential damage.
3. System Compromise
- Nature: Once exploited, the vulnerability could lead to the complete compromise of the affected system.
- Consequence: This includes potential installation of malware, backdoors, or other malicious tools, which could be used to further exploit or control the system.
4. Data Breach
- Nature: With unauthorized access, attackers can exfiltrate sensitive data.
- Consequence: This could result in the loss of confidential information, intellectual property, and personal data, leading to financial and reputational damage.
5. Service Disruption
- Nature: Exploitation of the vulnerability might lead to the disruption of services provided by the affected systems.
- Consequence: This can impact business operations, cause downtime, and affect service availability to users and clients.
6. Spread of Malware
- Nature: Compromised systems can be used as a launchpad for further attacks.
- Consequence: This can lead to the spread of malware within a network, affecting more systems and expanding the reach of the attack.
Mitigation and Patches
To mitigate the risks associated with CVE-2024-6387, the following steps should be taken:
- Patch and Update: Ensure all systems running affected versions of OpenSSH are updated to the latest patched version.
- Monitor and Audit: Regularly monitor and audit SSH access logs for any unusual activity.
- Access Controls: Implement strong access controls and use multi-factor authentication (MFA) to secure SSH access.
- Network Segmentation: Use network segmentation to limit the exposure of SSH services to potential attackers.
- Security Best Practices: Follow best practices for securing SSH, including using strong, unique passwords and disabling root login.
Information security specialist, currently working as risk infrastructure specialist & investigator.
15 years of experience in risk and control process, security audit support, business continuity design and support, workgroup management and information security standards.
