CVE-2025-40009: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability (CVE-2025-40009) was discovered in the Linux kernel's fs/proc/taskmmu component, specifically related to the PAGEMAPSCAN ioctl functionality. The vulnerability was disclosed on October 20, 2025, affecting various Linux distributions. The issue occurs when the PAGEMAPSCAN ioctl is invoked with veclen = 0, which can lead to a kernel panic due to a null pointer dereference (NVD).

The vulnerability manifests when veclen = 0 in pagemapscaninitbouncebuffer(), resulting in no buffers being allocated and p->vecbuf remaining set to NULL. This breaks an assumption in pagemapscanbackoutrange(), where pageregion is expected to always be allocated for p->vecbufindex. The issue leads to a kernel panic with a null pointer dereference at address 0xdffffc0000000000. According to the PAGEMAPSCAN man page, veclen = 0 is considered valid when no output is requested and only side effects are of interest (NVD).

The vulnerability can cause a kernel panic, leading to system instability and potential denial of service. The issue has been assigned a moderate severity rating with a CVSSv3 score of 7.0, indicating significant potential impact on system availability (RedHat).

The vulnerability has been fixed by explicitly checking p->vecbuf for NULL before dereferencing in the pagemapscanbackoutrange() function. The fix has been implemented across various Linux distributions, with Red Hat Enterprise Linux versions marking it as fixed in their security tracking system (RedHat).