riscv: lib: Fix ZBB strnlen reading past count boundary

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-74751
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-26 15:16:54 UTC
Updated2026-08-27 06:17:26 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: riscv: lib: Fix ZBB strnlen reading past count boundary The ZBB-optimized strnlen loop loads one word ahead before checking the aligned boundary: REG_L t1, SZREG(t0) // load next word addi t0, t0, SZREG // advance orc.b t1, t1 bgeu t0, t4, 4f // boundary check AFTER load where t4 = (s + count) & -SZREG. When s is aligned and count is a multiple of SZREG, t4 equals s + count and the loop loads a full word starting at exactly s + count. If s + count falls on a page boundary with the next page unmapped, this faults. Fix by computing the aligned boundary from the last valid byte (s + count - 1) instead of s + count. This makes the loop stop at the word containing the last valid byte rather than potentially loading the word after it. The count == 0 case is already handled by the beqz early exit. Also add a pre-loop guard (bgeu t0, t4) for the case where all valid bytes fit within the first word. With the adjusted boundary, t4 can equal t0, and entering the loop with stale register state from the first-word processing would produce incorrect results. The final minu clamp ensures the result is still correct when the last loaded word extends past s + count - 1 within the same aligned word.

Risk And Classification

Primary CVSS: v3.1 9.4 CRITICAL from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.003370000 probability, percentile 0.263030000 (date 2026-08-27)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary9.4CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:H
3.1CNADECLARED9.4CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:H

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 5ba15d419fab848a3813eb56bbcad00e291fbc49 e697e30f3dd2da3a1df7dc0980546d5b53aea4b6 git Not specified
CNA Linux Linux affected 5ba15d419fab848a3813eb56bbcad00e291fbc49 5d588c684833e678a0008eb69c33190f01a65f4b git Not specified
CNA Linux Linux affected 7.1 Not specified
CNA Linux Linux unaffected 7.1 semver Not specified
CNA Linux Linux unaffected 7.1.10 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/5d588c684833e678a0008eb69c33190f01a65f4b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e697e30f3dd2da3a1df7dc0980546d5b53aea4b6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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