CVE-2024-26798 is a vulnerability in the Linux kernel's framebuffer console (fbcon) subsystem, specifically related to the function fbcon_do_set_font(). The issue arises from improper restoration of font data when the virtual console resize operation (vc_resize()) fails. A prior commit (a5a923038d70) attempted to address this by restoring old font data upon failure, but this fix only applied to user fonts and neglected the system/internal fonts. Consequently, during the first invocation of fbcon_do_set_font(), if vc_resize() fails, the old font data is not restored, leading to a use-after-free or invalid memory access scenario. This flaw can cause a kernel crash manifested as a page fault in kernel mode, as demonstrated by a proof-of-concept crash triggered by Syzkaller with fault injection. The crash trace shows a supervisor read access violation due to referencing an invalid memory address during font retrieval operations. The root cause is that the old font data pointer is not properly restored for system fonts, which should always be reverted to maintain kernel stability. The fix involves restoring the font data unconditionally, not just for user fonts, ensuring that the kernel does not access freed or invalid memory after a failed resize operation. This vulnerability affects multiple Linux kernel versions identified by specific commit hashes and is relevant to systems using the framebuffer console interface for text display. Although exploitation requires triggering a failure in vc_resize(), which is not trivial, fault injection or fuzzing tools can facilitate this. No known exploits are reported in the wild as of the publication date.

For European organizations, the impact of CVE-2024-26798 primarily involves potential denial-of-service (DoS) conditions due to kernel crashes on affected Linux systems. Systems relying on framebuffer console for local or remote text-based management, embedded devices, or specialized Linux distributions using fbcon could experience unexpected reboots or service interruptions. This could affect critical infrastructure, industrial control systems, or servers where uptime and stability are paramount. Although this vulnerability does not directly lead to privilege escalation or remote code execution, the resulting kernel panic can disrupt operations, cause data loss, or trigger failover mechanisms. Organizations with Linux-based appliances or legacy systems that have not applied recent kernel patches are at risk. The difficulty in triggering the fault reduces the likelihood of widespread exploitation, but targeted attacks or automated fuzzing in hostile environments could exploit this flaw to degrade service availability.

To mitigate CVE-2024-26798, European organizations should: 1) Apply the latest Linux kernel patches that include the fix restoring font data unconditionally in fbcon_do_set_font(). This is the definitive solution to prevent the kernel crash. 2) For systems where immediate patching is not feasible, consider disabling framebuffer console usage or switching to alternative console drivers that do not rely on the vulnerable code path. 3) Implement kernel lockdown or integrity monitoring to detect abnormal kernel crashes and automate alerts for early incident response. 4) Employ fuzz testing and fault injection in controlled environments to proactively identify similar kernel vulnerabilities. 5) Maintain updated backups and failover strategies to minimize downtime in case of kernel panics. 6) Monitor security advisories from Linux distributions and vendors for backported fixes and apply them promptly. 7) Restrict access to systems that could trigger the vulnerability, limiting local user permissions and preventing untrusted code execution that might induce vc_resize() failures.