CVE-2026-45886
bpf: Fix bpf_xdp_store_bytes proto for read-only arg
Description
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.
INFO
Published Date :
May 27, 2026, 2:17 p.m.
Last Modified :
May 27, 2026, 2:48 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Solution
- Update the Linux kernel to resolve the vulnerability.
- Verify BPF program arguments and map access.
- Apply the corrected bpf_xdp_store_bytes proto.
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While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-45886 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
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stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-45886
weaknesses.
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New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 27, 2026
Action Type Old Value New Value Added Description 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. Added Reference https://git.kernel.org/stable/c/0db169a91381a473b7974021d1c02f8da72c5775 Added Reference https://git.kernel.org/stable/c/57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52 Added Reference https://git.kernel.org/stable/c/6557f1565d779851c4db9c488c49c05a47a6e72f Added Reference https://git.kernel.org/stable/c/d7b87adeb0eb539b9b824b101bb14fb01e41240b Added Reference https://git.kernel.org/stable/c/ddc34a1b85505c919026ddc82fafdada9a160b15 Added Reference https://git.kernel.org/stable/c/ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e