Linux: Use After Free
CVE-2022-49840 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 047824a730699c6c66df43306b80f700c9dfc2fd, 730fb1ef974a13915bc7651364d8b3318891cd70, 7a704dbfd3735304e261f2787c52fbc7c3884736 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 0.22% 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 047824a730699c6c66df43306b80f700c9dfc2fd or 730fb1ef974a13915bc7651364d8b3318891cd70 or 7a704dbfd3735304e261f2787c52fbc7c3884736 or e60f37a1d379c821c17b08f366412dce9ef3d99f, whichever matches your release line, or a later version.
- Update Linux Kernel to 4.14.300 or 4.19.267 or 5.4.225 or 5.10.156, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 1cf1cae963c2e6032aebe1637e995bc2f5d330f4 up to, but not including, 047824a730699c6c66df43306b80f700c9dfc2fd; 1cf1cae963c2e6032aebe1637e995bc2f5d330f4 up to, but not including, 730fb1ef974a13915bc7651364d8b3318891cd70; 1cf1cae963c2e6032aebe1637e995bc2f5d330f4 up to, but not including, 7a704dbfd3735304e261f2787c52fbc7c3884736; 1cf1cae963c2e6032aebe1637e995bc2f5d330f4 up to, but not including, e60f37a1d379c821c17b08f366412dce9ef3d99f; 1cf1cae963c2e6032aebe1637e995bc2f5d330f4 up to, but not including, eaa8edd86514afac9deb9bf9a5053e74f37edf40; 1cf1cae963c2e6032aebe1637e995bc2f5d330f4 up to, but not including, 1b597f2d6a55e9f549989913860ad5170da04964; 1cf1cae963c2e6032aebe1637e995bc2f5d330f4 up to, but not including, d3fd203f36d46aa29600a72d57a1b61af80e4a25; 4.12 | 047824a730699c6c66df43306b80f700c9dfc2fd, 730fb1ef974a13915bc7651364d8b3318891cd70, 7a704dbfd3735304e261f2787c52fbc7c3884736, e60f37a1d379c821c17b08f366412dce9ef3d99f, eaa8edd86514afac9deb9bf9a5053e74f37edf40, 1b597f2d6a55e9f549989913860ad5170da04964 |
| Linux | Linux Kernel | 4.12 up to, but not including, 4.14.300; 4.15 up to, but not including, 4.19.267; 4.20 up to, but not including, 5.4.225; 5.5 up to, but not including, 5.10.156; 5.11 up to, but not including, 5.15.80; 5.16 up to, but not including, 6.0.10; 6.1 | 4.14.300, 4.19.267, 5.4.225, 5.10.156, 5.15.80, 6.0.10 |
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 | NVD |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: bpf, test_run: Fix alignment problem in bpf_prog_test_run_skb() We got a syzkaller problem because of aarch64 alignment fault if KFENCE enabled. When the size from user bpf program is an odd number, like 399, 407, etc, it will cause the struct skb_shared_info's unaligned access. As seen below: BUG: KFENCE: use-after-free read in __skb_clone+0x23c/0x2a0 net/core/skbuff.c:1032 Use-after-free read at 0xffff6254fffac077 (in kfence-#213): __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:26 [inline] arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline] arch_atomic_inc include/linux/atomic-arch-fallback.h:270 [inline] atomic_inc include/asm-generic/atomic-instrumented.h:241 [inline] __skb_clone+0x23c/0x2a0 net/core/skbuff.c:1032 skb_clone+0xf4/0x214 net/core/skbuff.c:1481 ____bpf_clone_redirect net/core/filter.c:2433 [inline] bpf_clone_redirect+0x78/0x1c0 net/core/filter.c:2420 bpf_prog_d3839dd9068ceb51+0x80/0x330 bpf_dispatcher_nop_func include/linux/bpf.h:728 [inline] bpf_test_run+0x3c0/0x6c0 net/bpf/test_run.c:53 bpf_prog_test_run_skb+0x638/0xa7c net/bpf/test_run.c:594 bpf_prog_test_run kernel/bpf/syscall.c:3148 [inline] __do_sys_bpf kernel/bpf/syscall.c:4441 [inline] __se_sys_bpf+0xad0/0x1634 kernel/bpf/syscall.c:4381 kfence-#213: 0xffff6254fffac000-0xffff6254fffac196, size=407, cache=kmalloc-512 allocated by task 15074 on cpu 0 at 1342.585390s: kmalloc include/linux/slab.h:568 [inline] kzalloc include/linux/slab.h:675 [inline] bpf_test_init.isra.0+0xac/0x290 net/bpf/test_run.c:191 bpf_prog_test_run_skb+0x11c/0xa7c net/bpf/test_run.c:512 bpf_prog_test_run kernel/bpf/syscall.c:3148 [inline] __do_sys_bpf kernel/bpf/syscall.c:4441 [inline] __se_sys_bpf+0xad0/0x1634 kernel/bpf/syscall.c:4381 __arm64_sys_bpf+0x50/0x60 kernel/bpf/syscall.c:4381 To fix the problem, we adjust @size so that (@size + @hearoom) is a multiple of SMP_CACHE_BYTES. So we make sure the struct skb_shared_info is aligned to a cache line.
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/047824a730699c6c66df43306b80f700c9dfc2fd
- git.kernel.org/stable/c/1b597f2d6a55e9f549989913860ad5170da04964
- git.kernel.org/stable/c/730fb1ef974a13915bc7651364d8b3318891cd70
- git.kernel.org/stable/c/7a704dbfd3735304e261f2787c52fbc7c3884736
- git.kernel.org/stable/c/d3fd203f36d46aa29600a72d57a1b61af80e4a25
- git.kernel.org/stable/c/e60f37a1d379c821c17b08f366412dce9ef3d99f
- git.kernel.org/stable/c/eaa8edd86514afac9deb9bf9a5053e74f37edf40
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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