CVE-2025-40169 (GCVE-0-2025-40169)

Vulnerability from cvelistv5 – Published: 2025-11-12 10:46 – Updated: 2026-10-15 22:02
VLAI
Title
bpf: Reject negative offsets for ALU ops
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Reject negative offsets for ALU ops When verifying BPF programs, the check_alu_op() function validates instructions with ALU operations. The 'offset' field in these instructions is a signed 16-bit integer. The existing check 'insn->off > 1' was intended to ensure the offset is either 0, or 1 for BPF_MOD/BPF_DIV. However, because 'insn->off' is signed, this check incorrectly accepts all negative values (e.g., -1). This commit tightens the validation by changing the condition to '(insn->off != 0 && insn->off != 1)'. This ensures that any value other than the explicitly permitted 0 and 1 is rejected, hardening the verifier against malformed BPF programs.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-15 21:57 UTC
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7033 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: ec0e2da95f72d4a46050a4d994e4fe471474fd80 , < 3bce44b344040e5eef3d64d38b157c15304c0aab (git)
Affected: ec0e2da95f72d4a46050a4d994e4fe471474fd80 , < 5017c302ca4b2a45149ad64e058fa2d5623c068f (git)
Affected: ec0e2da95f72d4a46050a4d994e4fe471474fd80 , < 21167bf70dbe400563e189ac632258d35eda38b5 (git)
Affected: ec0e2da95f72d4a46050a4d994e4fe471474fd80 , < 55c0ced59fe17dee34e9dfd5f7be63cbab207758 (git)
guessed Create a notification for this product.
Linux Linux Affected: 6.6
Unaffected: 0 , < 6.6 (semver)
Unaffected: 6.6.112 , ≤ 6.6.* (semver)
Unaffected: 6.12.53 , ≤ 6.12.* (semver)
Unaffected: 6.17.3 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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              "value": "AV:L - The vulnerable code is reached through the local `bpf(BPF_PROG_LOAD)` syscall, which invokes `bpf_check()` \u2192 `do_check()` \u2192 `check_alu_op()`. Although the resulting program later executes on packet receive, loading the malformed instruction requires local system access.\nAC:L - Exploitation is fully deterministic: emit a `BPF_DIV`/`BPF_MOD` instruction with `off = -1`, set the dividend to `LLONG_MIN` and the divisor to `-1`, and run it. There is no race, no timing window, and no dependence on memory layout or system state the attacker cannot control.\nPR:L - `sysctl_unprivileged_bpf_disabled` defaults to 0 unless `CONFIG_BPF_UNPRIV_DEFAULT_OFF` is built in (Android and many embedded/distro configs leave it enabled), and `kernel/bpf/syscall.c:2941` explicitly permits `BPF_PROG_TYPE_SOCKET_FILTER` and `BPF_PROG_TYPE_CGROUP_SKB` loads with no `bpf_cap`; the program is then triggered via `SO_ATTACH_BPF` on the attacker\u0027s own socket. Where unprivileged BPF is disabled, `bpf_token_capable()` grants `ns_capable()`-level CAP_BPF inside a delegated user namespace, so real root is never required.\nUI:N - The attacker loads and triggers the BPF program entirely on their own, by attaching it to a socket they own and sending themselves a packet. No victim action of any kind is involved.\nS:U - The verifier bypass, the JIT\u0027d signed division, and the resulting fault all occur within the kernel\u0027s own security authority. No VM, IOMMU, or hypervisor boundary is crossed.\nC:H - On the s390 JIT the `switch (off)` in the DIV/MOD handlers has no default, so no divide instruction is emitted while the trailing `lgr %dst,%rc` still executes, copying the uninitialized kernel scratch register `%r0`/`%r1` \u2014 potentially a kernel pointer \u2014 into a BPF register that the program can write to a map and read from userspace, repeatably and at attacker-chosen program points. The x86 divide-error oops additionally dumps full register and stack state, defeating KASLR.\nI:H - The verifier accepts an instruction whose runtime semantics it never models \u2014 the JIT executes a signed division while the fixup layer applies only the unsigned guards, and on s390 uncontrolled kernel register contents are injected into verified program state. This is a verifier validation bypass in which JIT-emitted code and the verifier\u0027s model of that code diverge, so integrity of the sandbox\u0027s guarantees is not preserved.\nA:H - Because `is_sdiv`/`is_smod` in `do_misc_fixups()` test `insn-\u003eoff == 1`, the `LLONG_MIN sdiv -1` overflow guards are skipped while the x86-64 JIT still emits `cqo; idiv`, producing a #DE with no exception-table entry \u2014 `do_trap()` reaches `die(\"divide error\")`, oopsing the kernel. Triggered from a socket-filter/tc/XDP program this fires in softirq context, yielding \"Fatal exception in interrupt\" and a full system panic."
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject negative offsets for ALU ops\n\nWhen verifying BPF programs, the check_alu_op() function validates\ninstructions with ALU operations. The \u0027offset\u0027 field in these\ninstructions is a signed 16-bit integer.\n\nThe existing check \u0027insn-\u003eoff \u003e 1\u0027 was intended to ensure the offset is\neither 0, or 1 for BPF_MOD/BPF_DIV. However, because \u0027insn-\u003eoff\u0027 is\nsigned, this check incorrectly accepts all negative values (e.g., -1).\n\nThis commit tightens the validation by changing the condition to\n\u0027(insn-\u003eoff != 0 \u0026\u0026 insn-\u003eoff != 1)\u0027. This ensures that any value\nother than the explicitly permitted 0 and 1 is rejected, hardening the\nverifier against malformed BPF programs."
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            "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nbpf: Rechazar offsets negativos para operaciones ALU\n\nAl verificar programas BPF, la funci\u00f3n check_alu_op() valida instrucciones con operaciones ALU. El campo \u0027offset\u0027 en estas instrucciones es un entero con signo de 16 bits.\n\nLa comprobaci\u00f3n existente \u0027insn-\u003eoff \u003e 1\u0027 ten\u00eda la intenci\u00f3n de asegurar que el offset sea 0 o 1 para BPF_MOD/BPF_DIV. Sin embargo, debido a que \u0027insn-\u003eoff\u0027 tiene signo, esta comprobaci\u00f3n acepta incorrectamente todos los valores negativos (p. ej., -1).\n\nEste commit endurece la validaci\u00f3n al cambiar la condici\u00f3n a \u0027(insn-\u003eoff != 0 \u0026\u0026 insn-\u003eoff != 1)\u0027. Esto asegura que cualquier valor distinto de los 0 y 1 expl\u00edcitamente permitidos sea rechazado, endureciendo el verificador contra programas BPF malformados."
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                  "lessThanOrEqual": "6.17.*",
                  "status": "unaffected",
                  "version": "6.17.3",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "6.18",
                  "versionType": "original_commit_for_fix"
                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.6.112",
                      "versionStartIncluding": "6.6",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.12.53",
                      "versionStartIncluding": "6.6",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.17.3",
                      "versionStartIncluding": "6.6",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.18",
                      "versionStartIncluding": "6.6",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject negative offsets for ALU ops\n\nWhen verifying BPF programs, the check_alu_op() function validates\ninstructions with ALU operations. The \u0027offset\u0027 field in these\ninstructions is a signed 16-bit integer.\n\nThe existing check \u0027insn-\u003eoff \u003e 1\u0027 was intended to ensure the offset is\neither 0, or 1 for BPF_MOD/BPF_DIV. However, because \u0027insn-\u003eoff\u0027 is\nsigned, this check incorrectly accepts all negative values (e.g., -1).\n\nThis commit tightens the validation by changing the condition to\n\u0027(insn-\u003eoff != 0 \u0026\u0026 insn-\u003eoff != 1)\u0027. This ensures that any value\nother than the explicitly permitted 0 and 1 is rejected, hardening the\nverifier against malformed BPF programs."
            }
          ],
          "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 code is reached through the local `bpf(BPF_PROG_LOAD)` syscall, which invokes `bpf_check()` \u2192 `do_check()` \u2192 `check_alu_op()`. Although the resulting program later executes on packet receive, loading the malformed instruction requires local system access.\nAC:L - Exploitation is fully deterministic: emit a `BPF_DIV`/`BPF_MOD` instruction with `off = -1`, set the dividend to `LLONG_MIN` and the divisor to `-1`, and run it. There is no race, no timing window, and no dependence on memory layout or system state the attacker cannot control.\nPR:L - `sysctl_unprivileged_bpf_disabled` defaults to 0 unless `CONFIG_BPF_UNPRIV_DEFAULT_OFF` is built in (Android and many embedded/distro configs leave it enabled), and `kernel/bpf/syscall.c:2941` explicitly permits `BPF_PROG_TYPE_SOCKET_FILTER` and `BPF_PROG_TYPE_CGROUP_SKB` loads with no `bpf_cap`; the program is then triggered via `SO_ATTACH_BPF` on the attacker\u0027s own socket. Where unprivileged BPF is disabled, `bpf_token_capable()` grants `ns_capable()`-level CAP_BPF inside a delegated user namespace, so real root is never required.\nUI:N - The attacker loads and triggers the BPF program entirely on their own, by attaching it to a socket they own and sending themselves a packet. No victim action of any kind is involved.\nS:U - The verifier bypass, the JIT\u0027d signed division, and the resulting fault all occur within the kernel\u0027s own security authority. No VM, IOMMU, or hypervisor boundary is crossed.\nC:H - On the s390 JIT the `switch (off)` in the DIV/MOD handlers has no default, so no divide instruction is emitted while the trailing `lgr %dst,%rc` still executes, copying the uninitialized kernel scratch register `%r0`/`%r1` \u2014 potentially a kernel pointer \u2014 into a BPF register that the program can write to a map and read from userspace, repeatably and at attacker-chosen program points. The x86 divide-error oops additionally dumps full register and stack state, defeating KASLR.\nI:H - The verifier accepts an instruction whose runtime semantics it never models \u2014 the JIT executes a signed division while the fixup layer applies only the unsigned guards, and on s390 uncontrolled kernel register contents are injected into verified program state. This is a verifier validation bypass in which JIT-emitted code and the verifier\u0027s model of that code diverge, so integrity of the sandbox\u0027s guarantees is not preserved.\nA:H - Because `is_sdiv`/`is_smod` in `do_misc_fixups()` test `insn-\u003eoff == 1`, the `LLONG_MIN sdiv -1` overflow guards are skipped while the x86-64 JIT still emits `cqo; idiv`, producing a #DE with no exception-table entry \u2014 `do_trap()` reaches `die(\"divide error\")`, oopsing the kernel. Triggered from a socket-filter/tc/XDP program this fires in softirq context, yielding \"Fatal exception in interrupt\" and a full system panic."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T12:08:14.652Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/3bce44b344040e5eef3d64d38b157c15304c0aab"
            },
            {
              "url": "https://git.kernel.org/stable/c/5017c302ca4b2a45149ad64e058fa2d5623c068f"
            },
            {
              "url": "https://git.kernel.org/stable/c/21167bf70dbe400563e189ac632258d35eda38b5"
            },
            {
              "url": "https://git.kernel.org/stable/c/55c0ced59fe17dee34e9dfd5f7be63cbab207758"
            }
          ],
          "title": "bpf: Reject negative offsets for ALU ops",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2025-40169",
        "datePublished": "2025-11-12T10:46:51.736Z",
        "dateReserved": "2025-04-16T07:20:57.176Z",
        "dateUpdated": "2026-10-15T22:02:39.320Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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