A type confusion vulnerability in OpenSSL’s PKCS7_digest_from_attributes() function allows an attacker to cause a crash when the function processes a malformed PKCS#7 object. The code accesses an ASN1_TYPE union member without first validating that the type is V_ASN1_OCTET_STRING. If the type is different, the union points to invalid or NULL memory, leading to an invalid pointer dereference during signature verification, which in turn triggers a denial of service via application termination.

OpenSSL libraries on multiple releases—including 3.6, 3.5, 3.4, 3.3, 3.0, 1.1.1 and 1.0.2—are affected. Applications that perform PKCS#7 signature verification or call PKCS7_digest_from_attributes() directly are vulnerable. The FIPS modules in versions 3.5, 3.4, 3.3 and 3.0 are not impacted because the vulnerable parsing code lies outside the FIPS boundary.

With a CVSS score of 5.3 and an EPSS probability of less than 1 %, this issue is considered low severity and is not listed in CISA’s KEV catalog. Exploitation requires an attacker to supply a crafted, malformed signed PKCS#7 message to an application that processes it, typically through a remote interface that accepts signed data. Successful exploitation results in a crash, causing a denial of service without compromising confidentiality or integrity. Because the vulnerability is only triggered by specifically crafted input, attackers must have a vector to deliver the forged PKCS#7 data, such as a web service that accepts signed tokens.