Linux: Use After Free
CVE-2025-39866 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions e2a14bbae5d8bacaa301362744a110e2be40a3a3, b187c976111960e6e54a6b1fff724f6e3d39406c, 1edc2feb9c759a9883dfe81cb5ed231412d8b2e4 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.31% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to e2a14bbae5d8bacaa301362744a110e2be40a3a3 or b187c976111960e6e54a6b1fff724f6e3d39406c or 1edc2feb9c759a9883dfe81cb5ed231412d8b2e4 or bf89b1f87c72df79cf76203f71fbf8349cd5c9de, whichever matches your release line, or a later version.
- Update SIMATIC CN 4100 to V5.0 or a later version.
- Update Linux Kernel to 5.10.247 or 5.15.192 or 6.1.151 or 6.6.105, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 0747259d13febfcc838980a63c414c9b920cea6f up to, but not including, e2a14bbae5d8bacaa301362744a110e2be40a3a3; 0747259d13febfcc838980a63c414c9b920cea6f up to, but not including, b187c976111960e6e54a6b1fff724f6e3d39406c; 0747259d13febfcc838980a63c414c9b920cea6f up to, but not including, 1edc2feb9c759a9883dfe81cb5ed231412d8b2e4; 0747259d13febfcc838980a63c414c9b920cea6f up to, but not including, bf89b1f87c72df79cf76203f71fbf8349cd5c9de; 0747259d13febfcc838980a63c414c9b920cea6f up to, but not including, e63052921f1b25a836feb1500b841bff7a4a0456; 0747259d13febfcc838980a63c414c9b920cea6f up to, but not including, c8c14adf80bd1a6e4a1d7ee9c2a816881c26d17a; 0747259d13febfcc838980a63c414c9b920cea6f up to, but not including, d02d2c98d25793902f65803ab853b592c7a96b29; 4.2 | e2a14bbae5d8bacaa301362744a110e2be40a3a3, b187c976111960e6e54a6b1fff724f6e3d39406c, 1edc2feb9c759a9883dfe81cb5ed231412d8b2e4, bf89b1f87c72df79cf76203f71fbf8349cd5c9de, e63052921f1b25a836feb1500b841bff7a4a0456, c8c14adf80bd1a6e4a1d7ee9c2a816881c26d17a |
| Siemens | SIMATIC CN 4100 | before V5.0 | V5.0 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.5 and later; V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | V3.1.5 and later; V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | V3.1.5 and later; V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | V3.1.5 and later; V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | V3.1.5 and later; V3.1.6 and later; V3.1.7 and later | Not stated |
| Linux | Linux Kernel | 4.2 up to, but not including, 5.10.247; 5.11 up to, but not including, 5.15.192; 5.16 up to, but not including, 6.1.151; 6.2 up to, but not including, 6.6.105; 6.7 up to, but not including, 6.12.46; 6.13 up to, but not including, 6.16.6; 6.17 | 5.10.247, 5.15.192, 6.1.151, 6.6.105, 6.12.46, 6.16.6 |
| Debian | Debian Linux | 11.0 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: fs: writeback: fix use-after-free in __mark_inode_dirty() An use-after-free issue occurred when __mark_inode_dirty() get the bdi_writeback that was in the progress of switching. CPU: 1 PID: 562 Comm: systemd-random- Not tainted 6.6.56-gb4403bd46a8e #1 ...... pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : __mark_inode_dirty+0x124/0x418 lr : __mark_inode_dirty+0x118/0x418 sp : ffffffc08c9dbbc0 ........ Call trace: __mark_inode_dirty+0x124/0x418 generic_update_time+0x4c/0x60 file_modified+0xcc/0xd0 ext4_buffered_write_iter+0x58/0x124 ext4_file_write_iter+0x54/0x704 vfs_write+0x1c0/0x308 ksys_write+0x74/0x10c __arm64_sys_write+0x1c/0x28 invoke_syscall+0x48/0x114 el0_svc_common.constprop.0+0xc0/0xe0 do_el0_svc+0x1c/0x28 el0_svc+0x40/0xe4 el0t_64_sync_handler+0x120/0x12c el0t_64_sync+0x194/0x198 Root cause is: systemd-random-seed kworker ---------------------------------------------------------------------- ___mark_inode_dirty inode_switch_wbs_work_fn spin_lock(&inode->i_lock); inode_attach_wb locked_inode_to_wb_and_lock_list get inode->i_wb spin_unlock(&inode->i_lock); spin_lock(&wb->list_lock) spin_lock(&inode->i_lock) inode_io_list_move_locked spin_unlock(&wb->list_lock) spin_unlock(&inode->i_lock) spin_lock(&old_wb->list_lock) inode_do_switch_wbs spin_lock(&inode->i_lock) inode->i_wb = new_wb spin_unlock(&inode->i_lock) spin_unlock(&old_wb->list_lock) wb_put_many(old_wb, nr_switched) cgwb_release old wb released wb_wakeup_delayed() accesses wb, then trigger the use-after-free issue Fix this race condition by holding inode spinlock until wb_wakeup_delayed() finished.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/1edc2feb9c759a9883dfe81cb5ed231412d8b2e4
- git.kernel.org/stable/c/b187c976111960e6e54a6b1fff724f6e3d39406c
- git.kernel.org/stable/c/bf89b1f87c72df79cf76203f71fbf8349cd5c9de
- git.kernel.org/stable/c/c8c14adf80bd1a6e4a1d7ee9c2a816881c26d17a
- git.kernel.org/stable/c/d02d2c98d25793902f65803ab853b592c7a96b29
- git.kernel.org/stable/c/e2a14bbae5d8bacaa301362744a110e2be40a3a3
- git.kernel.org/stable/c/e63052921f1b25a836feb1500b841bff7a4a0456
Third-party and government advisories
- lists.debian.org/debian-lts-announce/2025/10/msg00008.htmlThird Party Advisory
Other references
Recent Use After Free vulnerabilities
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- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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