{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-43009", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-05-01T14:12:55.974Z", "datePublished": "2026-05-01T14:15:16.271Z", "dateUpdated": "2026-08-05T12:25:14.250Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:25:14.250Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix incorrect pruning due to atomic fetch precision tracking\n\nWhen backtrack_insn encounters a BPF_STX instruction with BPF_ATOMIC\nand BPF_FETCH, the src register (or r0 for BPF_CMPXCHG) also acts as\na destination, thus receiving the old value from the memory location.\n\nThe current backtracking logic does not account for this. It treats\natomic fetch operations the same as regular stores where the src\nregister is only an input. This leads the backtrack_insn to fail to\npropagate precision to the stack location, which is then not marked\nas precise!\n\nLater, the verifier's path pruning can incorrectly consider two states\nequivalent when they differ in terms of stack state. Meaning, two\nbranches can be treated as equivalent and thus get pruned when they\nshould not be seen as such.\n\nFix it as follows: Extend the BPF_LDX handling in backtrack_insn to\nalso cover atomic fetch operations via is_atomic_fetch_insn() helper.\nWhen the fetch dst register is being tracked for precision, clear it,\nand propagate precision over to the stack slot. For non-stack memory,\nthe precision walk stops at the atomic instruction, same as regular\nBPF_LDX. This covers all fetch variants.\n\nBefore:\n\n 0: (b7) r1 = 8 ; R1=8\n 1: (7b) *(u64 *)(r10 -8) = r1 ; R1=8 R10=fp0 fp-8=8\n 2: (b7) r2 = 0 ; R2=0\n 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) ; R2=8 R10=fp0 fp-8=mmmmmmmm\n 4: (bf) r3 = r10 ; R3=fp0 R10=fp0\n 5: (0f) r3 += r2\n mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1\n mark_precise: frame0: regs=r2 stack= before 4: (bf) r3 = r10\n mark_precise: frame0: regs=r2 stack= before 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2)\n mark_precise: frame0: regs=r2 stack= before 2: (b7) r2 = 0\n 6: R2=8 R3=fp8\n 6: (b7) r0 = 0 ; R0=0\n 7: (95) exit\n\nAfter:\n\n 0: (b7) r1 = 8 ; R1=8\n 1: (7b) *(u64 *)(r10 -8) = r1 ; R1=8 R10=fp0 fp-8=8\n 2: (b7) r2 = 0 ; R2=0\n 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) ; R2=8 R10=fp0 fp-8=mmmmmmmm\n 4: (bf) r3 = r10 ; R3=fp0 R10=fp0\n 5: (0f) r3 += r2\n mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1\n mark_precise: frame0: regs=r2 stack= before 4: (bf) r3 = r10\n mark_precise: frame0: regs=r2 stack= before 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2)\n mark_precise: frame0: regs= stack=-8 before 2: (b7) r2 = 0\n mark_precise: frame0: regs= stack=-8 before 1: (7b) *(u64 *)(r10 -8) = r1\n mark_precise: frame0: regs=r1 stack= before 0: (b7) r1 = 8\n 6: R2=8 R3=fp8\n 6: (b7) r0 = 0 ; R0=0\n 7: (95) exit" } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The vulnerable verifier logic is reached through the local bpf() syscall during BPF_PROG_LOAD, not by remote packets or adjacent/physical input.\nAC:L - An attacker controls the submitted BPF bytecode and can deterministically exercise atomic fetch precision tracking and verifier pruning; no race or external victim state is required.\nPR:L - The affected privileged verifier mode requires CAP_BPF/CAP_SYS_ADMIN or an equivalent BPF token, and this kernel supports BPF tokens/capability checks in user namespaces, making this reachable by a basic local user in plausible deployments.\nUI:N - Exploitation only requires the attacker to invoke bpf() with a crafted program; no separate victim action is needed.\nS:U - The impact is a standard kernel verifier bypass leading to kernel compromise within the same host security authority, not a VM/container boundary escape as a separate scope.\nC:H - Incorrect verifier pruning can allow unsafe pointer arithmetic and out-of-bounds BPF memory access; by analogy with similar verifier/runtime divergence bugs, this can provide kernel memory disclosure primitives.\nI:H - The verifier may accept a program whose unsafe path should have been rejected, enabling out-of-bounds writes or arbitrary kernel memory modification in the highest defensible exploitation scenario.\nA:H - Even without full read/write exploitation, accepted unsafe BPF memory accesses can crash or corrupt the kernel, causing a high availability impact." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "kernel/bpf/verifier.c" ], "versions": [ { "version": "5ca419f2864a2c60940dcf4bbaeb69546200e36f", "lessThan": "7ffbe45b1d227e24659998a91cfd4c27af457e71", "status": "affected", "versionType": "git" }, { "version": "5ca419f2864a2c60940dcf4bbaeb69546200e36f", "lessThan": "179ee84a89114b854ac2dd1d293633a7f6c8dac1", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "kernel/bpf/verifier.c" ], "versions": [ { "version": "5.12", "status": "affected" }, { "version": "0", "lessThan": "5.12", "status": "unaffected", "versionType": "semver" }, { "version": "6.19.12", "lessThanOrEqual": "6.19.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.0", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.12", "versionEndExcluding": "6.19.12" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.12", "versionEndExcluding": "7.0" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/7ffbe45b1d227e24659998a91cfd4c27af457e71" }, { "url": "https://git.kernel.org/stable/c/179ee84a89114b854ac2dd1d293633a7f6c8dac1" } ], "title": "bpf: Fix incorrect pruning due to atomic fetch precision tracking", "x_generator": { "engine": "bippy-1.2.0" } } } }