CVE-2026-22977: Medium Severity Vulnerability in Linux Kernel

In the Linux kernel, a vulnerability identified as CVE-2026-22977 has been resolved. This vulnerability allows for a potential kernel crash due to improper handling of usercopy operations when specific configurations are enabled.

The severity of this vulnerability is classified as medium, with a CVSS score of 5.5. This scoring highlights the importance of addressing the issue to prevent potential disruptions in system availability.

Risk to organizations includes potential system crashes and instability when userspace applications attempt to access kernel memory that has not been properly validated. The usercopy hardening mechanism can trigger a panic when the kernel tries to copy data from an unwhitelisted region.

This vulnerability has not been observed to have any public exploits or proof of concept code available. However, organizations are advised to monitor their systems and apply patches as they become available to mitigate risk.

Organizations should prioritize patching immediately.

Vulnerability Details

The vulnerability in question is described as follows: In the Linux kernel, the following vulnerability has been resolved: net: sock: fix hardened usercopy panic in sock_recv_errqueue. skbuff_fclone_cache was created without defining a usercopy region, unlike skbuff_head_cache which properly whitelists the cb[] field. This causes a usercopy BUG() when CONFIG_HARDENED_USERCOPY is enabled and the kernel attempts to copy sk_buff.cb data to userspace via sock_recv_errqueue() -> put_cmsg().

The crash occurs when: 1. TCP allocates an skb using alloc_skb_fclone() (from skbuff_fclone_cache) 2. The skb is cloned via skb_clone() using the pre-allocated fclone 3. The cloned skb is queued to sk_error_queue for timestamp reporting 4. Userspace reads the error queue via recvmsg(MSG_ERRQUEUE) 5. sock_recv_errqueue() calls put_cmsg() to copy serr->ee from skb->cb 6. __check_heap_object() fails because skbuff_fclone_cache has no usercopy whitelist.

This patch uses a local stack variable as a bounce buffer to avoid the hardened usercopy check failure.

Technical Analysis

The root cause of this vulnerability stems from the improper handling of usercopy regions when creating skbuff_fclone_cache. Specifically, the lack of a defined usercopy region leads to potential kernel memory exposure when attempting to access or copy data that has not been properly validated.

The attack vector is classified as local, meaning that an attacker would need to have local access to the system to exploit this vulnerability. The attack complexity is low, as it does not require advanced skills or knowledge to trigger the conditions that lead to a crash.

Privileges required to exploit this vulnerability are low, meaning that an attacker could potentially leverage this vulnerability without needing elevated permissions. User interaction is not required for this vulnerability to be exploited.

The impact on availability is high, as a successful exploitation of this vulnerability can lead to a denial of service through a kernel panic. There is no confidentiality or integrity impact associated with this vulnerability.

Risk & Impact Analysis

Real-world deployment risk associated with CVE-2026-22977 is significant in environments where the Linux kernel is utilized, particularly in production systems. The potential for kernel crashes due to improper usercopy handling poses a risk of system downtime and instability.

Organizations should assess their usage of affected versions of the Linux kernel and prioritize patching to mitigate the risks associated with this vulnerability. The blast radius potential is moderate, given that the impact is localized to systems running vulnerable versions of the Linux kernel.

Given the CVSS score of 5.5, organizations should address this vulnerability in their priority patch cycle. The absence of known exploits at this time does not diminish the need for timely remediation.

Exploitation Status

Affected Versions

The following versions of the Linux kernel are affected by this vulnerability:

All versions prior to vendor patch:

4.16 to below 5.10.248, 5.11 to below 5.15.198, 5.16 to below 6.1.161, 6.2 to below 6.6.121, 6.7 to below 6.12.66, 6.13 to below 6.18.6, and 6.19 release candidates.

Mitigation & Remediation

To mitigate this vulnerability, organizations should apply the relevant patches as soon as they become available. The following patches have been released:

Organizations should regularly check for updates and apply them to ensure system integrity. Additionally, implementing strict access controls and monitoring systems for unusual activity can help in detecting potential exploitation attempts.

For in-depth security assessments, organizations may consider utilizing penetration testing services to identify any potential vulnerabilities and ensure that defenses are robust.

Detection Guidance

Organizations should monitor system logs for indicators of exploitation attempts, including unusual access patterns or unexpected crashes. Behavioral anomalies in kernel operations should be investigated promptly.

AppSecure Threat Intelligence Insight

The long-term significance of CVE-2026-22977 lies in its representation of a category of vulnerabilities that can lead to significant disruptions in service availability, particularly in critical systems that rely on the Linux kernel.

Security teams should take this as a reminder of the importance of rigorous testing and validation of kernel-level changes to prevent similar vulnerabilities from being introduced in the future.

For ongoing education and updates, security teams are encouraged to follow best practices in penetration testing methodology and implement rigorous vulnerability management programs.