CVE-2026-5187: Heap Out-of-Bounds Write in DecodeObjectId() in wolfSSL

Vulnerability summary

CVE-2026-5187 is a critical (CVSS 9.8) Heap-based Buffer Overflow vulnerability in wolfssl. EPSS estimates a 0.28% chance of exploitation in the next 30 days, higher than 20.9% of scored vulnerabilities.

Timeline

1. 09-04-2026
   PublishedVulnerability first disclosed.
2. 14-04-2026
   Last modifiedVulnerability information updated.

Description

Two potential heap out-of-bounds write locations existed in DecodeObjectId() in wolfcrypt/src/asn.c. First, a bounds check only validates one available slot before writing two OID arc values (out[0] and out[1]), enabling a 2-byte out-of-bounds write when outSz equals 1. Second, multiple callers pass sizeof(decOid) (64 bytes on 64-bit platforms) instead of the element count MAX_OID_SZ (32), causing the function to accept crafted OIDs with 33 or more arcs that write past the end of the allocated buffer.

• CWE-122Heap-based Buffer OverflowThe product writes past the end of a buffer that was allocated on the heap.
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.