Linux: Use After Free
CVE-2022-50021 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 7550aade978371ac582f6d43b14c4cb89ca54463, 560a2744cbbf03cac65a6394f9b0d99aa437c867, a2522041d248a8c969cbbc97e1fc2cd8b4de120d 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 0.21% 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 7550aade978371ac582f6d43b14c4cb89ca54463 or 560a2744cbbf03cac65a6394f9b0d99aa437c867 or a2522041d248a8c969cbbc97e1fc2cd8b4de120d or 1e1c2b86ef86a8477fd9b9a4f48a6bfe235606f6, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.175 or 5.15.103 or 5.19.4, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 84130193e0e6568dfdfb823f0e1e19aec80aff6e up to, but not including, 7550aade978371ac582f6d43b14c4cb89ca54463; 84130193e0e6568dfdfb823f0e1e19aec80aff6e up to, but not including, 560a2744cbbf03cac65a6394f9b0d99aa437c867; 84130193e0e6568dfdfb823f0e1e19aec80aff6e up to, but not including, a2522041d248a8c969cbbc97e1fc2cd8b4de120d; 84130193e0e6568dfdfb823f0e1e19aec80aff6e up to, but not including, 1e1c2b86ef86a8477fd9b9a4f48a6bfe235606f6; 3.2 | 7550aade978371ac582f6d43b14c4cb89ca54463, 560a2744cbbf03cac65a6394f9b0d99aa437c867, a2522041d248a8c969cbbc97e1fc2cd8b4de120d, 1e1c2b86ef86a8477fd9b9a4f48a6bfe235606f6 |
| Linux | Linux Kernel | before 5.10.175; 5.11 up to, but not including, 5.15.103; 5.16 up to, but not including, 5.19.4 | 5.10.175, 5.15.103, 5.19.4 |
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.
Official description
In the Linux kernel, the following vulnerability has been resolved: ext4: block range must be validated before use in ext4_mb_clear_bb() Block range to free is validated in ext4_free_blocks() using ext4_inode_block_valid() and then it's passed to ext4_mb_clear_bb(). However in some situations on bigalloc file system the range might be adjusted after the validation in ext4_free_blocks() which can lead to troubles on corrupted file systems such as one found by syzkaller that resulted in the following BUG kernel BUG at fs/ext4/ext4.h:3319! PREEMPT SMP NOPTI CPU: 28 PID: 4243 Comm: repro Kdump: loaded Not tainted 5.19.0-rc6+ #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014 RIP: 0010:ext4_free_blocks+0x95e/0xa90 Call Trace: <TASK> ? lock_timer_base+0x61/0x80 ? __es_remove_extent+0x5a/0x760 ? __mod_timer+0x256/0x380 ? ext4_ind_truncate_ensure_credits+0x90/0x220 ext4_clear_blocks+0x107/0x1b0 ext4_free_data+0x15b/0x170 ext4_ind_truncate+0x214/0x2c0 ? _raw_spin_unlock+0x15/0x30 ? ext4_discard_preallocations+0x15a/0x410 ? ext4_journal_check_start+0xe/0x90 ? __ext4_journal_start_sb+0x2f/0x110 ext4_truncate+0x1b5/0x460 ? __ext4_journal_start_sb+0x2f/0x110 ext4_evict_inode+0x2b4/0x6f0 evict+0xd0/0x1d0 ext4_enable_quotas+0x11f/0x1f0 ext4_orphan_cleanup+0x3de/0x430 ? proc_create_seq_private+0x43/0x50 ext4_fill_super+0x295f/0x3ae0 ? snprintf+0x39/0x40 ? sget_fc+0x19c/0x330 ? ext4_reconfigure+0x850/0x850 get_tree_bdev+0x16d/0x260 vfs_get_tree+0x25/0xb0 path_mount+0x431/0xa70 __x64_sys_mount+0xe2/0x120 do_syscall_64+0x5b/0x80 ? do_user_addr_fault+0x1e2/0x670 ? exc_page_fault+0x70/0x170 entry_SYSCALL_64_after_hwframe+0x46/0xb0 RIP: 0033:0x7fdf4e512ace Fix it by making sure that the block range is properly validated before used every time it changes in ext4_free_blocks() or ext4_mb_clear_bb().
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: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Recent Use After Free vulnerabilities
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