CVE-2025-21887 ovl: fix UAF in ovl_dentry_update_reval by moving dput() in ovl_link_up
A use-after-free vulnerability in the Linux kernel's overlayfs allows local attackers to potentially execute arbitrary code or escalate privileges.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-21887?
CVE-2025-21887 is a high-severity use after free vulnerability in Linux kernel, published on 27 Mar 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ovl: fix UAF in ovl_dentry_update_reval by moving dput() in ovl_link_up
The issue was caused by dput(upper) being called before ovl_dentry_update_reval(), while upper->d_flags was still accessed in ovl_dentry_remote().
Move dput(upper) after its last use to prevent use-after-free.
BUG: KASAN: slab-use-after-free in ovl_dentry_remote fs/overlayfs/util.c:162 [inline] BUG: KASAN: slab-use-after-free in ovl_dentry_update_reval+0xd2/0xf0 fs/overlayfs/util.c:167
Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114 print_address_description mm/kasan/report.c:377 [inline] print_report+0xc3/0x620 mm/kasan/report.c:488 kasan_report+0xd9/0x110 mm/kasan/report.c:601 ovl_dentry_remote fs/overlayfs/util.c:162 [inline] ovl_dentry_update_reval+0xd2/0xf0 fs/overlayfs/util.c:167 ovl_link_up fs/overlayfs/copy_up.c:610 [inline] ovl_copy_up_one+0x2105/0x3490 fs/overlayfs/copy_up.c:1170 ovl_copy_up_flags+0x18d/0x200 fs/overlayfs/copy_up.c:1223 ovl_rename+0x39e/0x18c0 fs/overlayfs/dir.c:1136 vfs_rename+0xf84/0x20a0 fs/namei.c:4893 ... </TASK>
Weakness: CWE-416
Which versions are affected by CVE-2025-21887?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21887?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2025-21887 being exploited?
There is no known exploitation of CVE-2025-21887 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-59405, BELL-CVE-2025-21887, DEBIAN-CVE-2025-21887, GHSA-vjwm-w9rc-f4cc, ROOT-OS-DEBIAN-11-CVE-2025-21887, ROOT-OS-UBUNTU-2404-CVE-2025-21887 and 1 more.