CVE-2026-45886
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel, a vulnerability was found in the BPF helper function `bpf_xdp_store_bytes`. The expected argument type was incorrectly defined as `ARG_PTR_TO_UNINIT_MEM` with the `MEM_WRITE` flag, causing the BPF verifier to reject valid calls with read-only maps (BPF_F_RDONLY_PROG) and potentially allowing reads from uninitialized memory.
Risk Assessment
Organizations using BPF in Cilium or other programs may encounter verification errors when attempting to write to XDP packets using read-only maps, potentially breaking critical network functions.
Recommendation
Update the Linux kernel to a version containing the fix that changes the argument type to match `bpf_skb_store_bytes` (e.g., `ARG_PTR_TO_MEM` without `MEM_WRITE`). Check your kernel distributor for the patch availability.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix bpf_xdp_store_bytes proto for read-only arg While making some maps in Cilium read-only from the BPF side, we noticed that the bpf_xdp_store_bytes proto is incorrect. In particular, the verifier was throwing the following error: ; ret = ctx_store_bytes(ctx, l3_off + offsetof(struct iphdr, saddr), &nat->address, 4, 0); 635: (79) r1 = *(u64 *)(r10 -144) ; R1=ctx() R10=fp0 fp-144=ctx() 636: (b4) w2 = 26 ; R2=26 637: (b4) w4 = 4 ; R4=4 638: (b4) w5 = 0 ; R5=0 639: (85) call bpf_xdp_store_bytes#190 write into map forbidden, value_size=6 off=0 size=4 nat comes from a BPF_F_RDONLY_PROG map, so R3 is a PTR_TO_MAP_VALUE. The verifier checks the helper's memory access to R3 in check_mem_size_reg, as it reaches ARG_CONST_SIZE argument. The third argument has expected type ARG_PTR_TO_UNINIT_MEM, which includes the MEM_WRITE flag. The verifier thus checks for a BPF_WRITE access on R3. Given R3 points to a read-only map, the check fails. Conversely, ARG_PTR_TO_UNINIT_MEM can also lead to the helper reading from uninitialized memory. This patch simply fixes the expected argument type to match that of bpf_skb_store_bytes.