CyberSecBulletin
CVE-2023-52935NVD status: Analyzed

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2023-52935 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 352fbf61ce776fef18dca6a68680a6cd943dac95, cee956ab1efbd858b4ca61c8b474af5aa24b29a6, abdf3c33918185c3e8ffeb09ed3e334b3d7df47c 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 0.2% 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 352fbf61ce776fef18dca6a68680a6cd943dac95 or cee956ab1efbd858b4ca61c8b474af5aa24b29a6 or abdf3c33918185c3e8ffeb09ed3e334b3d7df47c or acb08187b5a83cdb9ac4112fae9e18cf983b0128, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.4.299 or 5.10.243 or 5.15.192 or 6.1.11, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxf3f0e1d2150b2b99da2cbdfaad000089efe9bf30 up to, but not including, 352fbf61ce776fef18dca6a68680a6cd943dac95; f3f0e1d2150b2b99da2cbdfaad000089efe9bf30 up to, but not including, cee956ab1efbd858b4ca61c8b474af5aa24b29a6; f3f0e1d2150b2b99da2cbdfaad000089efe9bf30 up to, but not including, abdf3c33918185c3e8ffeb09ed3e334b3d7df47c; f3f0e1d2150b2b99da2cbdfaad000089efe9bf30 up to, but not including, acb08187b5a83cdb9ac4112fae9e18cf983b0128; f3f0e1d2150b2b99da2cbdfaad000089efe9bf30 up to, but not including, 023f47a8250c6bdb4aebe744db4bf7f73414028b; 4.8352fbf61ce776fef18dca6a68680a6cd943dac95, cee956ab1efbd858b4ca61c8b474af5aa24b29a6, abdf3c33918185c3e8ffeb09ed3e334b3d7df47c, acb08187b5a83cdb9ac4112fae9e18cf983b0128, 023f47a8250c6bdb4aebe744db4bf7f73414028b
DebianDebian Linux11.0Not stated
LinuxLinux Kernel4.8 up to, but not including, 5.4.299; 5.5 up to, but not including, 5.10.243; 5.11 up to, but not including, 5.15.192; 5.16 up to, but not including, 6.1.11; 6.25.4.299, 5.10.243, 5.15.192, 6.1.11

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 CISA (ADP).

Official description

In the Linux kernel, the following vulnerability has been resolved: mm/khugepaged: fix ->anon_vma race If an ->anon_vma is attached to the VMA, collapse_and_free_pmd() requires it to be locked. Page table traversal is allowed under any one of the mmap lock, the anon_vma lock (if the VMA is associated with an anon_vma), and the mapping lock (if the VMA is associated with a mapping); and so to be able to remove page tables, we must hold all three of them. retract_page_tables() bails out if an ->anon_vma is attached, but does this check before holding the mmap lock (as the comment above the check explains). If we racily merged an existing ->anon_vma (shared with a child process) from a neighboring VMA, subsequent rmap traversals on pages belonging to the child will be able to see the page tables that we are concurrently removing while assuming that nothing else can access them. Repeat the ->anon_vma check once we hold the mmap lock to ensure that there really is no concurrent page table access. Hitting this bug causes a lockdep warning in collapse_and_free_pmd(), in the line "lockdep_assert_held_write(&vma->anon_vma->root->rwsem)". It can also lead to use-after-free access.

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. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Recent Use After Free vulnerabilities

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