bpf: Drop scalar id on sign-extending narrowing stack fills

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-93127
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 17:18:07 UTC
Updated2026-10-19 10:17:02 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: bpf: Drop scalar id on sign-extending narrowing stack fills When a spilled scalar is filled back with a sign-extending narrowing load (BPF_MEMSX), check_stack_read_fixed_off() copies the spilled register including its scalar id, but coerce_reg_to_size_sx() then sign-extends the filled register's value. If the same slot is also filled with a plain zero-extending load (BPF_MEM), both destination registers share the id yet hold different values. A later 'if <zext-reg> == const' then refines the sign-extended register through sync_linked_regs() to a value it does not have at runtime (e.g. the verifier believes 0x80000000 while the register is 0xffffffff80000000), which can be turned into an out-of-bounds access. Drop the shared scalar id at the sign-extension site in check_mem_access() when sign extension actually changes the value, mirroring the BPF_MOVSX handling in check_alu_op() (no_sext = reg_umax < 2^(size*8-1)).

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.001540000 probability, percentile 0.048970000 (date 2026-09-21)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 3cd5c890652ba1f0682adc291b5446245259b692 f3614622dc41f3dd99bb4f691da253814e4e6cae git Not specified
CNA Linux Linux affected 3cd5c890652ba1f0682adc291b5446245259b692 2cb5f4ca695ebe552647e5ba4aad6934d6a43bae git Not specified
CNA Linux Linux affected 7.0 Not specified
CNA Linux Linux unaffected 7.0 semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/2cb5f4ca695ebe552647e5ba4aad6934d6a43bae 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f3614622dc41f3dd99bb4f691da253814e4e6cae 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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