Linux: Use After Free
CVE-2022-49761 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 18bd1c9c02e64a3567f90c83c2c8b855531c8098, fdb4a70bb768d2a87890409597529ad81cb3de8a, 853ffa1511b058c79a4c9bb1407b3b20ce311792 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.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 18bd1c9c02e64a3567f90c83c2c8b855531c8098 or fdb4a70bb768d2a87890409597529ad81cb3de8a or 853ffa1511b058c79a4c9bb1407b3b20ce311792 or 39f501d68ec1ed5cd5c66ac6ec2a7131c517bb92, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.165 or 5.15.90 or 6.1.8, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 79787eaab46121d4713ed03c8fc63b9ec3eaec76 up to, but not including, 18bd1c9c02e64a3567f90c83c2c8b855531c8098; 79787eaab46121d4713ed03c8fc63b9ec3eaec76 up to, but not including, fdb4a70bb768d2a87890409597529ad81cb3de8a; 79787eaab46121d4713ed03c8fc63b9ec3eaec76 up to, but not including, 853ffa1511b058c79a4c9bb1407b3b20ce311792; 79787eaab46121d4713ed03c8fc63b9ec3eaec76 up to, but not including, 39f501d68ec1ed5cd5c66ac6ec2a7131c517bb92; 3.4 | 18bd1c9c02e64a3567f90c83c2c8b855531c8098, fdb4a70bb768d2a87890409597529ad81cb3de8a, 853ffa1511b058c79a4c9bb1407b3b20ce311792, 39f501d68ec1ed5cd5c66ac6ec2a7131c517bb92 |
| Linux | Linux Kernel | before 5.10.165; 5.11 up to, but not including, 5.15.90; 5.16 up to, but not including, 6.1.8; 6.2 | 5.10.165, 5.15.90, 6.1.8 |
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: btrfs: always report error in run_one_delayed_ref() Currently we have a btrfs_debug() for run_one_delayed_ref() failure, but if end users hit such problem, there will be no chance that btrfs_debug() is enabled. This can lead to very little useful info for debugging. This patch will: - Add extra info for error reporting Including: * logical bytenr * num_bytes * type * action * ref_mod - Replace the btrfs_debug() with btrfs_err() - Move the error reporting into run_one_delayed_ref() This is to avoid use-after-free, the @node can be freed in the caller. This error should only be triggered at most once. As if run_one_delayed_ref() failed, we trigger the error message, then causing the call chain to error out: btrfs_run_delayed_refs() `- btrfs_run_delayed_refs() `- btrfs_run_delayed_refs_for_head() `- run_one_delayed_ref() And we will abort the current transaction in btrfs_run_delayed_refs(). If we have to run delayed refs for the abort transaction, run_one_delayed_ref() will just cleanup the refs and do nothing, thus no new error messages would be output.
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.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Recent Use After Free vulnerabilities
- 7.8 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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