CVE-2026-43009 (GCVE-0-2026-43009)
Vulnerability from cvelistv5
Published
2026-05-01 14:15
Modified
2026-08-05 12:25
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
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
References
Impacted products
Vendor Product Version
Linux Linux Version: 5ca419f2864a2c60940dcf4bbaeb69546200e36f
Version: 5ca419f2864a2c60940dcf4bbaeb69546200e36f
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/verifier.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "7ffbe45b1d227e24659998a91cfd4c27af457e71",
              "status": "affected",
              "version": "5ca419f2864a2c60940dcf4bbaeb69546200e36f",
              "versionType": "git"
            },
            {
              "lessThan": "179ee84a89114b854ac2dd1d293633a7f6c8dac1",
              "status": "affected",
              "version": "5ca419f2864a2c60940dcf4bbaeb69546200e36f",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/verifier.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.12"
            },
            {
              "lessThan": "5.12",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.19.*",
              "status": "unaffected",
              "version": "6.19.12",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.0",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.19.12",
                  "versionStartIncluding": "5.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.0",
                  "versionStartIncluding": "5.12",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "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\u0027s 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": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "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."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:25:14.250Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-43009",
    "datePublished": "2026-05-01T14:15:16.271Z",
    "dateReserved": "2026-05-01T14:12:55.974Z",
    "dateUpdated": "2026-08-05T12:25:14.250Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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