CyberSecBulletin
CVE-2026-31702NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2026-31702 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 57bc678f36ac03281e877c6b84877b43f964143f, ef57cd3329b40c739b9a2e1a8a21ecc4171c6280, f5154cf3ce1c8193f0c1891d3769f62740cfe6fe 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 0.12% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 57bc678f36ac03281e877c6b84877b43f964143f or ef57cd3329b40c739b9a2e1a8a21ecc4171c6280 or f5154cf3ce1c8193f0c1891d3769f62740cfe6fe or c76cf339b87975ae5b2c06d2d774d5667d25a12a, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.6.136 or 6.12.84 or 6.18.25 or 7.0.2, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux4c8ff7095bef64fc47e996a938f7d57f9e077da3 up to, but not including, 57bc678f36ac03281e877c6b84877b43f964143f; 4c8ff7095bef64fc47e996a938f7d57f9e077da3 up to, but not including, ef57cd3329b40c739b9a2e1a8a21ecc4171c6280; 4c8ff7095bef64fc47e996a938f7d57f9e077da3 up to, but not including, f5154cf3ce1c8193f0c1891d3769f62740cfe6fe; 4c8ff7095bef64fc47e996a938f7d57f9e077da3 up to, but not including, c76cf339b87975ae5b2c06d2d774d5667d25a12a; 4c8ff7095bef64fc47e996a938f7d57f9e077da3 up to, but not including, 2c97dcb6147c8f7f25c629b93be1e69617de5d4a; 4c8ff7095bef64fc47e996a938f7d57f9e077da3 up to, but not including, 39d4ee19c1e7d753dd655aebee632271b171f43a; 5.657bc678f36ac03281e877c6b84877b43f964143f, ef57cd3329b40c739b9a2e1a8a21ecc4171c6280, f5154cf3ce1c8193f0c1891d3769f62740cfe6fe, c76cf339b87975ae5b2c06d2d774d5667d25a12a, 2c97dcb6147c8f7f25c629b93be1e69617de5d4a, 39d4ee19c1e7d753dd655aebee632271b171f43a
LinuxLinux Kernel5.6 up to, but not including, 6.6.136; 6.7 up to, but not including, 6.12.84; 6.13 up to, but not including, 6.18.25; 6.19 up to, but not including, 7.0.2; 7.16.6.136, 6.12.84, 6.18.25, 7.0.2

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.

Official description

In the Linux kernel, the following vulnerability has been resolved: f2fs: fix use-after-free of sbi in f2fs_compress_write_end_io() In f2fs_compress_write_end_io(), dec_page_count(sbi, type) can bring the F2FS_WB_CP_DATA counter to zero, unblocking f2fs_wait_on_all_pages() in f2fs_put_super() on a concurrent unmount CPU. The unmount path then proceeds to call f2fs_destroy_page_array_cache(sbi), which destroys sbi->page_array_slab via kmem_cache_destroy(), and eventually kfree(sbi). Meanwhile, the bio completion callback is still executing: when it reaches page_array_free(sbi, ...), it dereferences sbi->page_array_slab — a destroyed slab cache — to call kmem_cache_free(), causing a use-after-free. This is the same class of bug as CVE-2026-23234 (which fixed the equivalent race in f2fs_write_end_io() in data.c), but in the compressed writeback completion path that was not covered by that fix. Fix this by moving dec_page_count() to after page_array_free(), so that all sbi accesses complete before the counter decrement that can unblock unmount. For non-last folios (where atomic_dec_return on cic->pending_pages is nonzero), dec_page_count is called immediately before returning — page_array_free is not reached on this path, so there is no post-decrement sbi access. For the last folio, page_array_free runs while the F2FS_WB_CP_DATA counter is still nonzero (this folio has not yet decremented it), keeping sbi alive, and dec_page_count runs as the final operation.

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.

More Use After Free vulnerabilities (CWE-416)

Timeline

  1. CVE record published.
  2. Record last changed materially (score, affected products, status or references).

References

Recent Use After Free vulnerabilities

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