CVE-2026-31610: Medium Vulnerability in Linux Kernel

In the Linux kernel, a vulnerability has been identified that can lead to memory leaks. The issue arises during the handling of SPNEGO tokens in the ksmbd component. This vulnerability allows attackers to exploit slow memory leaks on a server without proper authentication, increasing the risk of resource exhaustion.

The severity of this vulnerability is classified as medium, with a CVSS score of 5.5. The attack vector is local, meaning that the exploitation requires local access to the system. Given the potential for resource exhaustion, organizations should prioritize patching this vulnerability.

Risk to organizations includes the possibility of untrusted clients exploiting the vulnerability to cause slow memory leaks, affecting system availability. Therefore, it is essential for defenders to address this vulnerability promptly.

Organizations should prioritize patching immediately to mitigate the risk associated with this vulnerability.

Vulnerability Details

The official description of this vulnerability details a leaking issue when SPNEGO decoding fails after token allocation. The vulnerability is described as follows: the kernel ASN.1 BER decoder calls action callbacks incrementally as it processes input. During this process, if a later element in the same blob is malformed, the decoder can return nonzero after the allocation is already live, leading to a memory leak.

The vulnerability is classified under CWE-401, indicating a memory leak. It affects the Linux kernel versions from 5.15 to below 6.6.136, 6.7 to below 6.12.83, 6.13 to below 6.18.24, 6.19 to below 6.19.14, and 7.0 to below 7.0.1.

The vulnerability was published on April 24, 2026, and is classified as having a medium severity due to the potential high availability impact.

Technical Analysis

The root cause of this vulnerability lies in the improper handling of memory allocation during the decoding of SPNEGO tokens. When the ksmbd_decode_negTokenInit() function encounters a malformed element, it fails to free the memory allocated for conn->mechToken, which can lead to persistent memory leaks.

The attack vector is local, requiring low privileges, and does not necessitate user interaction. This vulnerability has a low attack complexity, making it easier to exploit by untrusted clients.

The impacts on confidentiality and integrity are none, while the availability impact is high due to potential resource exhaustion on the server.

Risk & Impact Analysis

Real-world deployment of the affected Linux kernel versions poses significant risks. Organizations using these versions should be aware of the potential for untrusted clients to exploit this vulnerability and the resulting slow memory leaks that could lead to service degradation or outages.

Given the medium severity of this vulnerability, organizations should address it in their priority patch cycle to minimize the risk of availability impacts.

The urgency for organizations to remediate this vulnerability is high, as it can be exploited by untrusted clients without proper authentication.

Exploitation Status

Affected Versions

The affected versions of the Linux kernel include 5.15 to below 6.6.136, 6.7 to below 6.12.83, 6.13 to below 6.18.24, 6.19 to below 6.19.14, and 7.0 to below 7.0.1.

Mitigation & Remediation

Organizations should apply the latest patches provided by the Linux kernel developers to remediate this vulnerability. Patches addressing this issue can be found in the respective kernel update repositories.

If a patch is not immediately available, organizations should consider implementing configuration hardening and network controls to limit exposure to untrusted clients. Furthermore, continuous monitoring for signs of resource exhaustion should be established.

For further guidance, organizations can explore penetration testing services that can help identify similar vulnerabilities.

Detection Guidance

Organizations should monitor logs for indicators of resource exhaustion or memory leaks. Behavioral anomalies may also indicate exploitation attempts. Network signatures associated with SPNEGO token handling should be reviewed for potential unauthorized access.

AppSecure Threat Intelligence Insight

This vulnerability highlights the ongoing need for vigilance in the security of kernel components within Linux systems. It represents a continuing trend of vulnerabilities that can be exploited by unauthenticated users, emphasizing the importance of secure coding practices.

Security teams should learn from this incident to enhance their defensive strategies, focusing on thorough testing and validation of memory management in their applications.

For organizations looking to improve their security posture, exploring resources on penetration testing methodology and strategies can provide valuable insights.

Additionally, organizations should consider reviewing their vulnerability management program to ensure comprehensive coverage against similar threats.