A 1‑byte heap out‑of‑bounds read occurs in the OER decoding code generated by the ASN.1 compiler when it processes a maliciously crafted, zero‑length payload for a variable‑length, non‑negative integer type. The decoder does not verify that the required bytes exist before extracting the most significant bit, allowing a precise one‑byte read beyond the heap boundary. This flaw can be leveraged by an attacker to crash the application or cause downstream systems to interpret integer values incorrectly, potentially leading to protocol state compromises or logic bypass.

The vulnerability affects mouse07410’s ASN.1 compiler asn1c, versions 1.4 and earlier. The generated decoder code is commonly used to parse untrusted network inputs such as V2X vehicle‑to‑everything traffic, 5G telecom headers, or X.509 certificate structures.

The CVSS score of 8.2 indicates a medium‑to‑high severity. This issue is not listed in CISA’s KEV catalog, and no EPSS score is available, but the exploitation vector is network‑based: any untrusted OER‑formatted data sent to an application that uses asn1c‑generated code could trigger the flaw. The attacker’s ability to trigger a crash or alter integer values makes this a serious threat for services relying on robust decoding of network messages.