# CVE-2026-43009: bpf: Fix incorrect pruning due to atomic fetch precision tracking CVE-2026-43009 is fixed in 15 products on 1 platform, first by DEBIAN-CVE-2026-43009, released May 15, 2026. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2026-43009 - Priority: High - CVSS: 7.8 (Important) - EPSS: 0.0016 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: May 1, 2026 - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-43009 ## Description In the Linux kernel, the following vulnerability has been resolved: bpf: Fix incorrect pruning due to atomic fetch precision tracking When backtrack_insn encounters a BPF_STX instruction with BPF_ATOMIC and BPF_FETCH, the src register (or r0 for BPF_CMPXCHG) also acts as a destination, thus receiving the old value from the memory location. The current backtracking logic does not account for this. It treats atomic fetch operations the same as regular stores where the src register is only an input. This leads the backtrack_insn to fail to propagate precision to the stack location, which is then not marked as precise! Later, the verifier's path pruning can incorrectly consider two states equivalent when they differ in terms of stack state. Meaning, two branches can be treated as equivalent and thus get pruned when they should not be seen as such. Fix it as follows: Extend the BPF_LDX handling in backtrack_insn to also cover atomic fetch operations via is_atomic_fetch_insn() helper. When the fetch dst register is being tracked for precision, clear it, and propagate precision over to the stack slot. For non-stack memory, the precision walk stops at the atomic instruction, same as regular BPF_LDX. This covers all fetch variants. Before: 0: (b7) r1 = 8 ; R1=8 1: (7b) *(u64 *)(r10 -8) = r1 ; R1=8 R10=fp0 fp-8=8 2: (b7) r2 = 0 ; R2=0 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) ; R2=8 R10=fp0 fp-8=mmmmmmmm 4: (bf) r3 = r10 ; R3=fp0 R10=fp0 5: (0f) r3 += r2 mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1 mark_precise: frame0: regs=r2 stack= before 4: (bf) r3 = r10 mark_precise: frame0: regs=r2 stack= before 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) mark_precise: frame0: regs=r2 stack= before 2: (b7) r2 = 0 6: R2=8 R3=fp8 6: (b7) r0 = 0 ; R0=0 7: (95) exit After: 0: (b7) r1 = 8 ; R1=8 1: (7b) *(u64 *)(r10 -8) = r1 ; R1=8 R10=fp0 fp-8=8 2: (b7) r2 = 0 ; R2=0 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) ; R2=8 R10=fp0 fp-8=mmmmmmmm 4: (bf) r3 = r10 ; R3=fp0 R10=fp0 5: (0f) r3 += r2 mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1 mark_precise: frame0: regs=r2 stack= before 4: (bf) r3 = r10 mark_precise: frame0: regs=r2 stack= before 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) mark_precise: frame0: regs= stack=-8 before 2: (b7) r2 = 0 mark_precise: frame0: regs= stack=-8 before 1: (7b) *(u64 *)(r10 -8) = r1 mark_precise: frame0: regs=r1 stack= before 0: (b7) r1 = 8 6: R2=8 R3=fp8 6: (b7) r0 = 0 ; R0=0 7: (95) exit ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | kernel-64kb sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-64kb sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-azure sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-azure sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-default sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-default sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-default-base sles 15.7 | 6.4.0-150700.53.55.1.150700.17.33.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-default-base sles 16.0 | 6.12.0-160000.34.1.160000.2.15 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-docs sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-docs sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-kvmsmall sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-livepatch-SLE15-SP7-RT_Update_16 sles 15.7 | 1-150700.1.5.2 | [SUSE-SU-2026:2591-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2591-1.md) | Jun 23, 2026 | | Linux | kernel-livepatch-SLE15-SP7_Update_15 sles 15.7 | 1-150700.15.3.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-livepatch-SLE15-SP7_Update_16 sles 15.7 | 1-150700.15.3.2 | [SUSE-SU-2026:2482-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2482-1.md) | Jun 22, 2026 | | Linux | kernel-obs-build sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-obs-qa sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-source sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-source sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-syms sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-syms sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | kernel-zfcpdump sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-zfcpdump sles 16.0 | 6.12.0-160000.34.1 | [SUSE-SU-2026:22087-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22087-1.md) | Jun 5, 2026 | | Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-43009](https://patchblox.com/security/data/fix/linux/debian-cve-2026-43009.md) | May 15, 2026 | | Linux | linux Debian 14 | 6.19.12-1 | [DEBIAN-CVE-2026-43009](https://patchblox.com/security/data/fix/linux/debian-cve-2026-43009.md) | May 15, 2026 | --- Data as of 2026-11-08T06:59:42Z UTC. 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