CyberSecBulletin
CVE-2022-49834NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2022-49834 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 b2fbf10040216ef5ee270773755fc2f5da65b749, 39a3ed68270b079c6b874d4e4727a512b9b4882c, b4736ab5542112fe0a40f140a0a0b072954f34da 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 0.22% 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 b2fbf10040216ef5ee270773755fc2f5da65b749 or 39a3ed68270b079c6b874d4e4727a512b9b4882c or b4736ab5542112fe0a40f140a0a0b072954f34da or 9b162e81045266a2d5b44df9dffdf05c54de9cca, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 4.9.334 or 4.14.300 or 4.19.267 or 5.4.225, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxfe5f171bb272946ce5fbf843ce2f8467d0d41b9a up to, but not including, b2fbf10040216ef5ee270773755fc2f5da65b749; fe5f171bb272946ce5fbf843ce2f8467d0d41b9a up to, but not including, 39a3ed68270b079c6b874d4e4727a512b9b4882c; fe5f171bb272946ce5fbf843ce2f8467d0d41b9a up to, but not including, b4736ab5542112fe0a40f140a0a0b072954f34da; fe5f171bb272946ce5fbf843ce2f8467d0d41b9a up to, but not including, 9b162e81045266a2d5b44df9dffdf05c54de9cca; fe5f171bb272946ce5fbf843ce2f8467d0d41b9a up to, but not including, 4feedde5486c07ea79787839153a71ca71329c7d; fe5f171bb272946ce5fbf843ce2f8467d0d41b9a up to, but not including, afbd1188382a75f6cfe22c0b68533f7f9664f182; fe5f171bb272946ce5fbf843ce2f8467d0d41b9a up to, but not including, b152300d5a1ba4258dacf9916bff20e6a8c7603b; fe5f171bb272946ce5fbf843ce2f8467d0d41b9a up to, but not including, 8cccf05fe857a18ee26e20d11a8455a73ffd4efd; and 1 more rangesb2fbf10040216ef5ee270773755fc2f5da65b749, 39a3ed68270b079c6b874d4e4727a512b9b4882c, b4736ab5542112fe0a40f140a0a0b072954f34da, 9b162e81045266a2d5b44df9dffdf05c54de9cca, 4feedde5486c07ea79787839153a71ca71329c7d, afbd1188382a75f6cfe22c0b68533f7f9664f182
LinuxLinux Kernelbefore 4.9.334; 4.10 up to, but not including, 4.14.300; 4.15 up to, but not including, 4.19.267; 4.20 up to, but not including, 5.4.225; 5.5 up to, but not including, 5.10.155; 5.11 up to, but not including, 5.15.79; 5.16 up to, but not including, 6.0.9; 6.14.9.334, 4.14.300, 4.19.267, 5.4.225, 5.10.155, 5.15.79

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 systemScoreSeverityScored by
CVSS 3.17.8HighCNA
CVSS 3.17.8HighNVD

Official description

In the Linux kernel, the following vulnerability has been resolved: nilfs2: fix use-after-free bug of ns_writer on remount If a nilfs2 filesystem is downgraded to read-only due to metadata corruption on disk and is remounted read/write, or if emergency read-only remount is performed, detaching a log writer and synchronizing the filesystem can be done at the same time. In these cases, use-after-free of the log writer (hereinafter nilfs->ns_writer) can happen as shown in the scenario below: Task1 Task2 -------------------------------- ------------------------------ nilfs_construct_segment nilfs_segctor_sync init_wait init_waitqueue_entry add_wait_queue schedule nilfs_remount (R/W remount case) nilfs_attach_log_writer nilfs_detach_log_writer nilfs_segctor_destroy kfree finish_wait _raw_spin_lock_irqsave __raw_spin_lock_irqsave do_raw_spin_lock debug_spin_lock_before <-- use-after-free While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After Task1 waked up, Task1 accesses nilfs->ns_writer which is already freed. This scenario diagram is based on the Shigeru Yoshida's post [1]. This patch fixes the issue by not detaching nilfs->ns_writer on remount so that this UAF race doesn't happen. Along with this change, this patch also inserts a few necessary read-only checks with superblock instance where only the ns_writer pointer was used to check if the filesystem is read-only.

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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