CVE-2022-49961 bpf: Do mark_chain_precision for ARG_CONST_ALLOC_SIZE_OR_ZERO
A flaw in the Linux kernel BPF verifier allows out-of-bounds memory access, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2022-49961?
CVE-2022-49961 is a high-severity memory corruption vulnerability in Linux kernel, published on 18 Jun 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
bpf: Do mark_chain_precision for ARG_CONST_ALLOC_SIZE_OR_ZERO
Precision markers need to be propagated whenever we have an ARG_CONST_* style argument, as the verifier cannot consider imprecise scalars to be equivalent for the purposes of states_equal check when such arguments refine the return value (in this case, set mem_size for PTR_TO_MEM). The resultant mem_size for the R0 is derived from the constant value, and if the verifier incorrectly prunes states considering them equivalent where such arguments exist (by seeing that both registers have reg->precise as false in regsafe), we can end up with invalid programs passing the verifier which can do access beyond what should have been the correct mem_size in that explored state.
To show a concrete example of the problem:
0000000000000000 <prog>: 0: r2 = *(u32 *)(r1 + 80) 1: r1 = *(u32 *)(r1 + 76) 2: r3 = r1 3: r3 += 4 4: if r3 > r2 goto +18 <LBB5_5> 5: w2 = 0 6: *(u32 *)(r1 + 0) = r2 7: r1 = *(u32 *)(r1 + 0) 8: r2 = 1 9: if w1 == 0 goto +1 <LBB5_3> 10: r2 = -1
0000000000000058 <LBB5_3>: 11: r1 = 0 ll 13: r3 = 0 14: call bpf_ringbuf_reserve 15: if r0 == 0 goto +7 <LBB5_5> 16: r1 = r0 17: r1 += 16777215 18: w2 = 0 19: *(u8 *)(r1 + 0) = r2 20: r1 = r0 21: r2 = 0 22: call bpf_ringbuf_submit
00000000000000b8 <LBB5_5>: 23: w0 = 0 24: exit
For the first case, the single line execution's exploration will prune the search at insn 14 for the branch insn 9's second leg as it will be verified first using r2 = -1 (UINT_MAX), while as w1 at insn 9 will always be 0 so at runtime we don't get error for being greater than UINT_MAX/4 from bpf_ringbuf_reserve. The verifier during regsafe just sees reg->precise as false for both r2 registers in both states, hence considers them equal for purposes of states_equal.
If we propagated precise markers using the backtracking support, we would use the precise marking to then ensure that old r2 (UINT_MAX) was within the new r2 (1) and this would never be true, so the verification would rightfully fail.
The end result is that the out of bounds access at instruction 19 would be permitted without this fix.
Note that reg->precise is always set to true when user does not have CAP_BPF (or when subprog count is greater than 1 (i.e. use of any static or global functions)), hence this is only a problem when precision marks need to be explicitly propagated (i.e. privileged users with CAP_BPF).
A simplified test case has been included in the next patch to prevent future regressions.
Weakness: CWE-125
Which versions are affected by CVE-2022-49961?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2022-49961?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2022-49961 being exploited?
There is no known exploitation of CVE-2022-49961 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-70214, DEBIAN-CVE-2022-49961, GHSA-34r5-4vr6-q5h6, ROOT-OS-DEBIAN-11-CVE-2022-49961, ROOT-OS-UBUNTU-2204-CVE-2022-49961, UBUNTU-CVE-2022-49961.