Linux: Use After Free
CVE-2022-50488 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 5533742c7cb1bc9b1f0bf401cc397d44a3a9e07a, 094f3d9314d67691cb21ba091c1b528f6e3c4893, b22fd72bfebda3956efc4431b60ddfc0a51e03e0 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 0.17% 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 5533742c7cb1bc9b1f0bf401cc397d44a3a9e07a or 094f3d9314d67691cb21ba091c1b528f6e3c4893 or b22fd72bfebda3956efc4431b60ddfc0a51e03e0 or 761564d93c8265f65543acf0a576b32d66bfa26a, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.5 or 5.10.175 or 5.15.86 or 5.18, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 4dfc12f8c94c8052e975060f595938f75e8b7165 up to, but not including, 5533742c7cb1bc9b1f0bf401cc397d44a3a9e07a; 81b7d0c717a487ec50e2924a773ff501ee40f0d5 up to, but not including, 094f3d9314d67691cb21ba091c1b528f6e3c4893; 3bc5e683c67d94bd839a1da2e796c15847b51b69 up to, but not including, b22fd72bfebda3956efc4431b60ddfc0a51e03e0; 3bc5e683c67d94bd839a1da2e796c15847b51b69 up to, but not including, 761564d93c8265f65543acf0a576b32d66bfa26a; 3bc5e683c67d94bd839a1da2e796c15847b51b69 up to, but not including, 64dc8c732f5c2b406cc752e6aaa1bd5471159cab; 31326bf551269fb9bafa84ca99172b8340e5d8f8; 43c51b86dbe551cff5d39b88aa2f41d29479f9c4; 8615f6c0c9e7cf0ca90b6b5408784d797cbe5621; and 6 more ranges | 5533742c7cb1bc9b1f0bf401cc397d44a3a9e07a, 094f3d9314d67691cb21ba091c1b528f6e3c4893, b22fd72bfebda3956efc4431b60ddfc0a51e03e0, 761564d93c8265f65543acf0a576b32d66bfa26a, 64dc8c732f5c2b406cc752e6aaa1bd5471159cab, 5.10.175 |
| Linux | Linux Kernel | 5.4.198 up to, but not including, 5.5; 5.10.121 up to, but not including, 5.10.175; 5.15.46 up to, but not including, 5.15.86; 5.17.14 up to, but not including, 5.18; 5.18.3 up to, but not including, 6.0.16; 6.1 up to, but not including, 6.1.2 | 5.5, 5.10.175, 5.15.86, 5.18, 6.0.16, 6.1.2 |
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: block, bfq: fix possible uaf for 'bfqq->bic' Our test report a uaf for 'bfqq->bic' in 5.10: ================================================================== BUG: KASAN: use-after-free in bfq_select_queue+0x378/0xa30 CPU: 6 PID: 2318352 Comm: fsstress Kdump: loaded Not tainted 5.10.0-60.18.0.50.h602.kasan.eulerosv2r11.x86_64 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-20220320_160524-szxrtosci10000 04/01/2014 Call Trace: bfq_select_queue+0x378/0xa30 bfq_dispatch_request+0xe8/0x130 blk_mq_do_dispatch_sched+0x62/0xb0 __blk_mq_sched_dispatch_requests+0x215/0x2a0 blk_mq_sched_dispatch_requests+0x8f/0xd0 __blk_mq_run_hw_queue+0x98/0x180 __blk_mq_delay_run_hw_queue+0x22b/0x240 blk_mq_run_hw_queue+0xe3/0x190 blk_mq_sched_insert_requests+0x107/0x200 blk_mq_flush_plug_list+0x26e/0x3c0 blk_finish_plug+0x63/0x90 __iomap_dio_rw+0x7b5/0x910 iomap_dio_rw+0x36/0x80 ext4_dio_read_iter+0x146/0x190 [ext4] ext4_file_read_iter+0x1e2/0x230 [ext4] new_sync_read+0x29f/0x400 vfs_read+0x24e/0x2d0 ksys_read+0xd5/0x1b0 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x61/0xc6 Commit 3bc5e683c67d ("bfq: Split shared queues on move between cgroups") changes that move process to a new cgroup will allocate a new bfqq to use, however, the old bfqq and new bfqq can point to the same bic: 1) Initial state, two process with io in the same cgroup. Process 1 Process 2 (BIC1) (BIC2) | Λ | Λ | | | | V | V | bfqq1 bfqq2 2) bfqq1 is merged to bfqq2. Process 1 Process 2 (BIC1) (BIC2) | | \-------------\| V bfqq1 bfqq2(coop) 3) Process 1 exit, then issue new io(denoce IOA) from Process 2. (BIC2) | Λ | | V | bfqq2(coop) 4) Before IOA is completed, move Process 2 to another cgroup and issue io. Process 2 (BIC2) Λ |\--------------\ | V bfqq2 bfqq3 Now that BIC2 points to bfqq3, while bfqq2 and bfqq3 both point to BIC2. If all the requests are completed, and Process 2 exit, BIC2 will be freed while there is no guarantee that bfqq2 will be freed before BIC2. Fix the problem by clearing bfqq->bic while bfqq is detached from bic.
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
- git.kernel.org/stable/c/094f3d9314d67691cb21ba091c1b528f6e3c4893
- git.kernel.org/stable/c/5533742c7cb1bc9b1f0bf401cc397d44a3a9e07a
- git.kernel.org/stable/c/64dc8c732f5c2b406cc752e6aaa1bd5471159cab
- git.kernel.org/stable/c/761564d93c8265f65543acf0a576b32d66bfa26a
- git.kernel.org/stable/c/b22fd72bfebda3956efc4431b60ddfc0a51e03e0
Recent Use After Free vulnerabilities
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- 7.8 High severity
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