CVE-2025-68292: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-68292 is an information disclosure vulnerability in the Linux kernel's mm/memfd subsystem, specifically affecting the allocation of hugetlb folios for memfd. When allocating these folios, three critical initialization steps are skipped: folios are not zeroed before use, they are not marked uptodate before being added to the page cache, and the hugetlb_fault_mutex is not acquired before calling hugetlb_add_to_page_cache(). This allows uninitialized kernel memory to be disclosed to userspace, particularly through read() or mmap() operations on the memfd, and is especially dangerous in udmabuf use cases where folios are pinned and accessed via DMA. The vulnerability was published on December 16, 2025, and affects Linux kernel versions from commit 89c1905d9c14 up to the patched releases. It carries a CVSS v3.1 base score of 7.0 (High) (Red Hat Advisory, Red Hat Bugzilla).

The root cause is classified as an improper initialization flaw (CWE-909 / uninitialized memory use) in the Linux kernel's mm/memfd.c. The memfd hugetlb allocation path bypasses the normal page fault handler hugetlb_no_page(), which is responsible for zeroing folios, marking them uptodate, and serializing page cache insertion with hugetlb_fault_mutex. Without these steps, newly allocated hugetlb folios may contain residual kernel memory data. An attacker with local access and low privileges can create a memfd backed by hugetlb pages and then read or mmap the file to access uninitialized kernel memory contents. The fix aligns the allocation path with hugetlb_no_page() by calling folio_zero_user(), folio_mark_uptodate(), and taking hugetlb_fault_mutex before hugetlb_add_to_page_cache() (Red Hat Bugzilla).

Successful exploitation allows a local, low-privileged user to read uninitialized kernel memory, potentially exposing sensitive data such as cryptographic keys, passwords, or other process memory contents that were previously resident in the kernel's huge page allocator. In udmabuf scenarios, the impact is amplified because pinned folios are directly accessible to userspace via DMA, bypassing normal memory isolation. The CVSS score also reflects high integrity and availability impacts (score 7.0), suggesting that the missing mutex could additionally lead to race conditions with potential for memory corruption (Red Hat Advisory, Red Hat Bugzilla).

1. Gain local access: Obtain a low-privileged shell on a vulnerable Linux system running a kernel version between commit 89c1905d9c14 and the patched releases (before 6.12.61, 6.17.11, or 6.18).
2. Create a hugetlb-backed memfd: Use the memfd_create() syscall with MFD_HUGETLB flag to create a memory file descriptor backed by huge pages.
3. Allocate pages without initialization: Write to or fault in pages of the memfd, triggering the vulnerable allocation path that skips zeroing and mutex acquisition.
4. Read uninitialized memory: Use read() or mmap() on the memfd to access the allocated hugetlb folios, which may contain residual kernel memory from prior allocations.
5. Extract sensitive data: Scan the returned memory for patterns corresponding to cryptographic material, kernel pointers, or other sensitive data structures (Red Hat Bugzilla).

• Process Behavior: Unusual processes repeatedly calling memfd_create() with MFD_HUGETLB flags followed by large read() or mmap() operations on the resulting file descriptor.
• Logs: Kernel audit logs (auditd) showing repeated memfd_create syscalls with hugetlb flags from non-privileged user processes.
• System: Unexpected consumption of huge pages (/proc/meminfo showing elevated HugePages_Rsvd or HugePages_Free fluctuations) by unprivileged processes.
• File System: Presence of /proc/<pid>/fd entries pointing to memfd files with hugetlb backing from suspicious or unknown processes.

The Linux kernel has released patches addressing this vulnerability in stable branches. Fixed versions include kernel 6.12.61, 6.17.11, and 6.18 (mainline). Patch commits are available at 50b4c1c28733, b09d7c4dc642, and de8798965fd0 in the stable kernel tree. Ubuntu has issued security notices USN-8094-1 through USN-8094-5 and USN-8152-1 addressing this issue. Red Hat has tracked the issue via Bugzilla #2422803. Users should update to a patched kernel version as soon as possible; no configuration-based workaround is available short of disabling hugetlb memfd usage if operationally feasible (Red Hat Advisory, Ubuntu USN-8094-1, Red Hat Bugzilla).

Red Hat tracked the vulnerability at medium severity via their Bugzilla system, and Ubuntu issued multiple security notices (USN-8094-1 through USN-8094-5, USN-8152-1) addressing the flaw across different kernel variants. Detection signatures have been added by Qualys and Tenable (Nessus plugin IDs 302766 and 304219), indicating standard industry response. No notable researcher commentary or significant social media discussion has been identified beyond routine vendor advisory activity (Ubuntu USN-8094-1, Red Hat Bugzilla).