CVE-2026-74751
CriticalCVSS 9.4Exploitation Probability (EPSS)
Low risk26th percentile - higher than 26% of all known CVEs
Summary
In the Linux kernel for RISC-V, the ZBB-optimized strnlen loop may read one word past the count boundary when the start address is aligned and count is a multiple of word size. This can cause a page fault if the next page is unmapped.
Risk Assessment
The vulnerability could lead to a system crash (kernel panic) due to improper memory read. It may be exploited to cause denial of service.
Recommendation
Install a Linux kernel patch that changes the aligned boundary calculation based on the last valid byte (s + count - 1) and adds a pre-loop guard for the case where all bytes fit within the first word.
Other vulnerabilities in Linux kernel
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Original NVD description (English source)
In 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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS