CVE-2025-21694: Medium Vulnerability in Linux Kernel

In the Linux kernel, a vulnerability has been resolved that affects the handling of softlockups during crash dumps. This issue arises in the __read_vmcore function, which has seen improvements since commit 5cbcb62dddf5. However, instances of softlockups still occur, particularly in memory-constrained environments such as kdump images. A softlockup can hinder RCU memory freeing processes, potentially causing the crashdump to become unresponsive.

The vulnerability is classified with a CVSS score of 5.5, indicating a medium severity level. The attack vector is local, with a low attack complexity and low privileges required. Consequently, defenders should address this vulnerability promptly, as the impact on availability is assessed to be high.

Organizations should prioritize patching immediately to mitigate risks associated with this vulnerability. The urgency is underscored by the potential for system crashes during critical operations.

Currently, there are no public exploits available, and this vulnerability is not included in the Known Exploited Vulnerabilities (KEV) catalog. Nevertheless, maintaining an updated kernel is crucial for mitigating potential risks.

In summary, this vulnerability poses a risk to organizations, particularly those utilizing the affected versions of the Linux kernel in high-availability environments. Organizations should evaluate their exposure and apply relevant patches to reduce potential impact.

Vulnerability Details

The vulnerability is described as follows: In the Linux kernel, the following vulnerability has been resolved: fs/proc: fix softlockup in __read_vmcore (part 2) Since commit 5cbcb62dddf5 ("fs/proc: fix softlockup in __read_vmcore") the number of softlockups in __read_vmcore at kdump time have gone down, but they still happen sometimes.

In a memory constrained environment like the kdump image, a softlockup is not just a harmless message, but it can interfere with things like RCU freeing memory, causing the crashdump to get stuck.

The second loop in __read_vmcore has a lot more opportunities for natural sleep points, like scheduling out while waiting for a data write to happen, but apparently that is not always enough.

Add a cond_resched() to the second loop in __read_vmcore to (hopefully) get rid of the softlockups.

Technical Analysis

Root cause analysis indicates that the softlockups occur during the crash dumping process, particularly when memory resources are constrained. The attack vector is local, which means attackers would need physical or console access to the target system. The attack complexity is low; hence, it could be executed with minimal effort.

In terms of privileges required, this vulnerability necessitates low privileges, allowing a user with limited access to potentially exploit it. Importantly, user interaction is not required for this vulnerability to be triggered, which increases its risk profile.

The impact on confidentiality and integrity is none, but the availability impact is assessed as high, meaning that exploitation could lead to system unavailability, thereby affecting critical operations.

Risk & Impact Analysis

Organizations using affected versions of the Linux kernel must consider the real-world deployment risk associated with this vulnerability. The potential for a softlockup during critical operations can result in significant downtime, impacting business continuity.

The blast radius for this vulnerability is substantial, especially for organizations that operate in environments where uptime is critical. Given the medium severity rating and the high availability impact, organizations should prioritize addressing this vulnerability in their patch management cycles.

Based on the CVSS score and the lack of known exploits, organizations are advised to schedule remediation during their next patch cycle. The urgency to patch is moderate, but the implications of unaddressed vulnerabilities remain significant.

Exploitation Status

Affected Versions

Affected versions of the Linux kernel include: 4.19.317 to below 4.20, 5.4.279 to below 5.4.290, 5.10.221 to below 5.10.234, 5.15.162 to below 5.15.177, 6.1.95 to below 6.1.127, and 6.6.35 to below 6.6.74, as well as several release candidates of version 6.13.

Mitigation & Remediation

Organizations should apply the latest patches to their Linux kernel installations to remediate this vulnerability. For applications that rely on specific kernel versions, upgrading to a version beyond the vulnerable ranges is critical. If an immediate patch is unavailable, consider implementing configuration hardening and monitoring for any unusual system behavior during kdump operations.

For more in-depth guidance on secure configurations and monitoring recommendations, organizations may consider reviewing our resources on secure configuration management.

Detection Guidance

To detect potential exploitation attempts related to this vulnerability, organizations should focus on log indicators that highlight kdump operations and RCU memory freeing processes. Monitoring for behavioral anomalies during crash dump operations can also provide insights into potential issues arising from softlockups.

AppSecure Threat Intelligence Insight

This vulnerability highlights the ongoing challenges within the Linux kernel to manage system resources effectively during critical operations. As systems become increasingly complex, the potential for softlockups may rise. Organizations should ensure that they have robust monitoring and incident response strategies in place to mitigate the impact of similar vulnerabilities in the future.

For further reading on vulnerability management best practices, organizations can refer to our blog on vulnerability management programs and for insights on penetration testing methodologies, please check our article on penetration testing methodology.

Additionally, reviewing our guide on AI penetration testing can provide organizations with insights on leveraging advanced technologies to enhance security testing.