CVE-2025-40271
Published Dec 6, 2025
Last updated 24 days ago
AI description
CVE-2025-40271 is a use-after-free (UAF) vulnerability found in the Linux kernel, specifically within the `proc_readdir_de()` function of the `/proc` filesystem. This flaw is a race condition that occurs when a `proc_dir_entry` is freed but its corresponding rbtree node is not properly cleared, leading to a lingering reference. A local attacker with low privileges can exploit this vulnerability by simultaneously traversing specific directories while network devices are being unregistered. This concurrent activity can trigger the use-after-free condition, potentially resulting in information disclosure, privilege escalation, or a denial of service.
- Description
- In the Linux kernel, the following vulnerability has been resolved: fs/proc: fix uaf in proc_readdir_de() Pde is erased from subdir rbtree through rb_erase(), but not set the node to EMPTY, which may result in uaf access. We should use RB_CLEAR_NODE() set the erased node to EMPTY, then pde_subdir_next() will return NULL to avoid uaf access. We found an uaf issue while using stress-ng testing, need to run testcase getdent and tun in the same time. The steps of the issue is as follows: 1) use getdent to traverse dir /proc/pid/net/dev_snmp6/, and current pde is tun3; 2) in the [time windows] unregister netdevice tun3 and tun2, and erase them from rbtree. erase tun3 first, and then erase tun2. the pde(tun2) will be released to slab; 3) continue to getdent process, then pde_subdir_next() will return pde(tun2) which is released, it will case uaf access. CPU 0 | CPU 1 ------------------------------------------------------------------------- traverse dir /proc/pid/net/dev_snmp6/ | unregister_netdevice(tun->dev) //tun3 tun2 sys_getdents64() | iterate_dir() | proc_readdir() | proc_readdir_de() | snmp6_unregister_dev() pde_get(de); | proc_remove() read_unlock(&proc_subdir_lock); | remove_proc_subtree() | write_lock(&proc_subdir_lock); [time window] | rb_erase(&root->subdir_node, &parent->subdir); | write_unlock(&proc_subdir_lock); read_lock(&proc_subdir_lock); | next = pde_subdir_next(de); | pde_put(de); | de = next; //UAF | rbtree of dev_snmp6 | pde(tun3) / \ NULL pde(tun2)
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- NVD status
- Deferred
- Hype score
- Not currently trending
A Linux kernel proc readdir use after free (CVE-2025-40271) allows local privilege escalation. Fixed in 5.10.247, 6.1.159, and 6.18-rc6. https://t.co/j0wIOTapmZ #CVE #LinuxKernel #UseAfterFree #LocalPrivilegeEscalation #procfs #getdents64 #KernelExploit #InfoSec #LinuxSecurity
@redsecuretech
6 May 2026
282 Impressions
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CVE-2025-40271 exploits Linux kernel proc_readdir_de() use-after-free in kernels ~3.14+ through 6.18-rc5. Race condition in /proc filesystem allows local privilege escalation via rb-tree traversal of freed proc entries. Technical details: • remove_proc_entry() calls rb_erase()
@DFIR_Radar
4 May 2026
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CVE-2025-40271 In the Linux kernel, the following vulnerability has been resolved: fs/proc: fix uaf in proc_readdir_de() Pde is erased from subdir rbtree through rb_erase(), but n… https://t.co/DWEIow0imZ
@CVEnew
6 Dec 2025
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