Linux: Use After Free
CVE-2022-50095 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 541840859ace9c2ccebc32fa9e376c7bd3def490, 9e255ed238fc67058df87b0388ad6d4b2ef3a2bd, e8cb6e8fd9890780f1bfcf5592889e1b879e779c 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 0.27% 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 541840859ace9c2ccebc32fa9e376c7bd3def490 or 9e255ed238fc67058df87b0388ad6d4b2ef3a2bd or e8cb6e8fd9890780f1bfcf5592889e1b879e779c or b2fc1723eb65abb83e00d5f011de670296af0b28, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.137 or 5.15.61 or 5.18.18 or 5.19.2, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 up to, but not including, 541840859ace9c2ccebc32fa9e376c7bd3def490; 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 up to, but not including, 9e255ed238fc67058df87b0388ad6d4b2ef3a2bd; 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 up to, but not including, e8cb6e8fd9890780f1bfcf5592889e1b879e779c; 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 up to, but not including, b2fc1723eb65abb83e00d5f011de670296af0b28; 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 up to, but not including, e362359ace6f87c201531872486ff295df306d13; 5.7 | 541840859ace9c2ccebc32fa9e376c7bd3def490, 9e255ed238fc67058df87b0388ad6d4b2ef3a2bd, e8cb6e8fd9890780f1bfcf5592889e1b879e779c, b2fc1723eb65abb83e00d5f011de670296af0b28, e362359ace6f87c201531872486ff295df306d13 |
| Linux | Linux Kernel | 5.7 up to, but not including, 5.10.137; 5.11 up to, but not including, 5.15.61; 5.16 up to, but not including, 5.18.18; 5.19 up to, but not including, 5.19.2 | 5.10.137, 5.15.61, 5.18.18, 5.19.2 |
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.
| 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: posix-cpu-timers: Cleanup CPU timers before freeing them during exec Commit 55e8c8eb2c7b ("posix-cpu-timers: Store a reference to a pid not a task") started looking up tasks by PID when deleting a CPU timer. When a non-leader thread calls execve, it will switch PIDs with the leader process. Then, as it calls exit_itimers, posix_cpu_timer_del cannot find the task because the timer still points out to the old PID. That means that armed timers won't be disarmed, that is, they won't be removed from the timerqueue_list. exit_itimers will still release their memory, and when that list is later processed, it leads to a use-after-free. Clean up the timers from the de-threaded task before freeing them. This prevents a reported use-after-free.
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.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/541840859ace9c2ccebc32fa9e376c7bd3def490
- git.kernel.org/stable/c/9e255ed238fc67058df87b0388ad6d4b2ef3a2bd
- git.kernel.org/stable/c/b2fc1723eb65abb83e00d5f011de670296af0b28
- git.kernel.org/stable/c/e362359ace6f87c201531872486ff295df306d13
- git.kernel.org/stable/c/e8cb6e8fd9890780f1bfcf5592889e1b879e779c
Recent Use After Free vulnerabilities
- 8.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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