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CVE Record

CVE-2026-31413: bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR

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.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux kernel BPF verifier mistake can approve behavior that differs from what the processor actually executes. A local attacker with low privileges may use that mismatch to access memory outside a BPF map’s bounds, threatening system confidentiality, integrity, and availability.

Executive priority

Prioritize assessment and patching because successful local exploitation could compromise all three security objectives. Focus first on multi-user or otherwise locally accessible Linux systems. Exact exposure cannot be determined from the supplied version data alone, so require vendor-confirmed affected-build mapping before closing findings.

Technical view

For BPF_OR with a constant operand and destination range [-1, 0], maybe_fork_scalars() incorrectly models the forked zero path as remaining zero, although 0 | K equals K. This verifier/runtime divergence permits out-of-bounds map access. The fix makes the pushed path re-execute the ALU instruction at the current instruction index.

Likely exposure

Potential exposure includes Linux hosts running an affected kernel where a low-privileged actor can reach BPF program loading. The bundle does not define exact vulnerable ranges, configuration prerequisites, or distribution backports. Its listed versions and hashes are marked defaultStatus unaffected, so version-only matching is insufficient; consult distribution or vendor mappings.

Exploitation context

The kernel description explicitly calls the verifier/runtime divergence exploitable and says it allows out-of-bounds map access. CVSS characterizes exploitation as local, low complexity, low privilege, and requiring no user interaction. The CVE is not listed as KEV, and the supplied sources provide no evidence of active exploitation.

Researcher notes

The source establishes an unsound verifier state fork for BPF_OR and identifies instruction re-execution as the correction. No CWE is assigned. The supplied affected data is insufficient for definitive vulnerable-version boundaries and marks its listed entries defaultStatus unaffected. No exploit sample, configuration prerequisite, distribution mapping, or in-the-wild activity is documented.

Mitigation direction

  • Apply a vendor-supported kernel update containing the applicable referenced stable fix.
  • Check Linux distribution advisories for affected build and backport mappings.
  • Prioritize shared systems where low-privileged accounts or services can load BPF programs.
  • Use vendor-recommended restrictions as temporary mitigation if an update cannot be applied promptly.

Validation and detection

  • Inventory running kernel versions and distribution build identifiers across Linux hosts.
  • Check vendor changelogs or kernel source trees for the applicable referenced fix commit.
  • Identify low-privileged accounts or services permitted to load BPF programs.
  • Confirm remediated kernels are running after required restart procedures.
  • Run relevant vendor or kernel BPF verifier regression tests after updating.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2026-31413 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
0ADP providers
5Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2026-31413Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxdea9989a3f3961faede93752cd81eb5a9514d911, 4c122e8ae14950cf6b59d208fc5160f7c601e746, e52567173ba86dbffb990595fbe60e2e83899372, bffacdb80b93b7b5e96b26fad64cc490a6c7d6c7unaffected
LinuxLinux6.12.75, 6.18.16, 6.19.6unaffected
Weakness

CWE details

No CWE listed

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