The vulnerability is a stack buffer overflow that occurs during verification of PKCS#7 signatures in osslsigncode. When verifying PE, MSI, CAB, or script files, the code copies a digest from SpcIndirectDataContent into a 64‑byte stack buffer without checking the source length. An attacker can create a malicious signed file containing an oversized digest. When a user runs osslsigncode verify on this file, the unbounded memcpy overflows the stack, corrupting adjacent data and potentially allowing arbitrary code to be executed or the application to crash. The weakness is a classic stack-based buffer overflow (CWE‑121) and an unvalidated memory copy (CWE‑787).

Vendor mtrojnar’s osslsigncode tool is affected. Any release prior to version 2.12 is vulnerable. The fix was released in the 2.12 release and subsequent versions should contain the patch. Systems that rely on osslsigncode for signing or verifying Authenticode, PKCS#7 signatures, or timestamping are at risk when processing untrusted binary or script files.

The CVSS base score is 7.8, indicating high severity. No EPSS score is available and the vulnerability is not listed in the CISA KEV catalog, suggesting that it has not yet seen widespread exploitation. However, the attack requires an attacker to supply a crafted signed file and a user to invoke osslsigncode verify, which is a local or remote file‑based exploitation scenario. Because the stack corruption can lead to arbitrary code execution, the risk remains significant for environments that routinely verify signatures from untrusted sources.