CVE-2026-62381: openwrt luci Heap-based Buffer Overflow

Vulnerability summary

CVE-2026-62381 is a medium (CVSS 6.9) Heap-based Buffer Overflow vulnerability in openwrt luci. EPSS estimates a 0.11% chance of exploitation in the next 30 days, higher than 1.1% of scored vulnerabilities.

Timeline

1. 22-08-2026
   PublishedVulnerability first disclosed.
2. 24-08-2026
   Last modifiedVulnerability information updated.

Description

luci-lib-px5g (LuCI) contains a heap-based buffer overflow in the native ASN.1 encoding routine asn1_add_obj (x509write.c) when signing a certificate with a 2040-bit RSA key. For a 255-byte signature, the BIT STRING allocation is computed from the DER length encoding of 255 bytes, but the payload written after prepending the unused-bits byte is 256 bytes, requiring one additional DER length octet. As a result the allocation is 259 bytes while the tag, length, unused-bits byte, and signature require 260 bytes, and the final memcpy writes one byte beyond the heap buffer. The overflow is reachable through the exported Lua interface via create_selfsigned(); whether it is remotely exploitable depends on the embedding application. The vulnerable code is present on the openwrt-18.06 through openwrt-25.12 release branches and is absent from master, where the luci-lib-px5g package has been removed rather than patched.

• CWE-122Heap-based Buffer OverflowA heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().