CyberSecBulletin
CVE-2022-49647NVD status: Analyzed

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2022-49647 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 05f7658210d1d331e8dd4cb6e7bbbe3df5f5ac27, cec2bbdcc14fbaa6b95ee15a7c423b05d97038be, ad44e05f3e016bdcb1ad25af35ade5b5f41ccd68 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 0.29% 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 05f7658210d1d331e8dd4cb6e7bbbe3df5f5ac27 or cec2bbdcc14fbaa6b95ee15a7c423b05d97038be or ad44e05f3e016bdcb1ad25af35ade5b5f41ccd68 or 7657e3958535d101a24ab4400f9b8062b9107cc4, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 4.14.289 or 4.19.253 or 5.4.207 or 5.10.132, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxf817de98513d060023be4fa1d061b29a6515273e up to, but not including, 05f7658210d1d331e8dd4cb6e7bbbe3df5f5ac27; f817de98513d060023be4fa1d061b29a6515273e up to, but not including, cec2bbdcc14fbaa6b95ee15a7c423b05d97038be; f817de98513d060023be4fa1d061b29a6515273e up to, but not including, ad44e05f3e016bdcb1ad25af35ade5b5f41ccd68; f817de98513d060023be4fa1d061b29a6515273e up to, but not including, 7657e3958535d101a24ab4400f9b8062b9107cc4; f817de98513d060023be4fa1d061b29a6515273e up to, but not including, 54aee4e5ce8c21555286a6333e46c1713880cf93; f817de98513d060023be4fa1d061b29a6515273e up to, but not including, 0e41774b564befa6d271e8d5086bf870d617a4e6; f817de98513d060023be4fa1d061b29a6515273e up to, but not including, 07fd5b6cdf3cc30bfde8fe0f644771688be04447; 3.1605f7658210d1d331e8dd4cb6e7bbbe3df5f5ac27, cec2bbdcc14fbaa6b95ee15a7c423b05d97038be, ad44e05f3e016bdcb1ad25af35ade5b5f41ccd68, 7657e3958535d101a24ab4400f9b8062b9107cc4, 54aee4e5ce8c21555286a6333e46c1713880cf93, 0e41774b564befa6d271e8d5086bf870d617a4e6
LinuxLinux Kernel3.16 up to, but not including, 4.14.289; 4.15 up to, but not including, 4.19.253; 4.20 up to, but not including, 5.4.207; 5.5 up to, but not including, 5.10.132; 5.11 up to, but not including, 5.15.56; 5.16 up to, but not including, 5.18.13; 5.194.14.289, 4.19.253, 5.4.207, 5.10.132, 5.15.56, 5.18.13

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: cgroup: Use separate src/dst nodes when preloading css_sets for migration Each cset (css_set) is pinned by its tasks. When we're moving tasks around across csets for a migration, we need to hold the source and destination csets to ensure that they don't go away while we're moving tasks about. This is done by linking cset->mg_preload_node on either the mgctx->preloaded_src_csets or mgctx->preloaded_dst_csets list. Using the same cset->mg_preload_node for both the src and dst lists was deemed okay as a cset can't be both the source and destination at the same time. Unfortunately, this overloading becomes problematic when multiple tasks are involved in a migration and some of them are identity noop migrations while others are actually moving across cgroups. For example, this can happen with the following sequence on cgroup1: #1> mkdir -p /sys/fs/cgroup/misc/a/b #2> echo $$ > /sys/fs/cgroup/misc/a/cgroup.procs #3> RUN_A_COMMAND_WHICH_CREATES_MULTIPLE_THREADS & #4> PID=$! #5> echo $PID > /sys/fs/cgroup/misc/a/b/tasks #6> echo $PID > /sys/fs/cgroup/misc/a/cgroup.procs the process including the group leader back into a. In this final migration, non-leader threads would be doing identity migration while the group leader is doing an actual one. After #3, let's say the whole process was in cset A, and that after #4, the leader moves to cset B. Then, during #6, the following happens: 1. cgroup_migrate_add_src() is called on B for the leader. 2. cgroup_migrate_add_src() is called on A for the other threads. 3. cgroup_migrate_prepare_dst() is called. It scans the src list. 4. It notices that B wants to migrate to A, so it tries to A to the dst list but realizes that its ->mg_preload_node is already busy. 5. and then it notices A wants to migrate to A as it's an identity migration, it culls it by list_del_init()'ing its ->mg_preload_node and putting references accordingly. 6. The rest of migration takes place with B on the src list but nothing on the dst list. This means that A isn't held while migration is in progress. If all tasks leave A before the migration finishes and the incoming task pins it, the cset will be destroyed leading to use-after-free. This is caused by overloading cset->mg_preload_node for both src and dst preload lists. We wanted to exclude the cset from the src list but ended up inadvertently excluding it from the dst list too. This patch fixes the issue by separating out cset->mg_preload_node into ->mg_src_preload_node and ->mg_dst_preload_node, so that the src and dst preloadings don't interfere with each other.

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

Recent Use After Free vulnerabilities

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