OpenSSL Out-of-bounds Write Vulnerability - CVE-2025-69419

Issue summary: Calling PKCS12_get_friendlyname() function on a maliciously crafted PKCS12 file with a BMPString (UTF-16BE) friendly name containing non-ASCII BMP code point can trigger a one byte write before the allocated buffer. Impact summary: The out-of-bounds write can cause a memory corruption which can have various consequences including a Denial of Service. The OPENSSL_uni2utf8() function performs a two-pass conversion of a PKCS12 BMPString (UTF-16BE) to UTF-8. In the second pass when emitting UTF-8 bytes the helper function bmp_to_utf8() incorrectly forwards the remaining UTF-16 source byte count as the destination buffer capacity to UTF8_putc(). For BMP code points above U07FF UTF-8 requires three bytes but the forwarded capacity can be just two bytes. UTF8_putc() then returns -1 and this negative value is added to the output length without validation causing the length to become negative. The subsequent trailing NUL byte is then written at a negative offset causing write outside of heap allocated buffer. The vulnerability is reachable via the public PKCS12_get_friendlyname() API when parsing attacker-controlled PKCS12 files. While PKCS12_parse() uses a different code path that avoids this issue PKCS12_get_friendlyname() directly invokes the vulnerable function. Exploitation requires an attacker to provide a malicious PKCS12 file to be parsed by the application and the attacker can just trigger a one zero byte write before the allocated buffer. For that reason the issue was assessed as Low severity according to our Security Policy. The FIPS modules in 3.6 3.5 3.4 3.3 and 3.0 are not affected by this issue as the PKCS12 implementation is outside the OpenSSL FIPS module boundary. OpenSSL 3.6 3.5 3.4 3.3 3.0 and 1.1.1 are vulnerable to this issue. OpenSSL 1.0.2 is not affected by this issue.