CVE-2022-4450

The function PEM_read_bio_ex() reads a PEM file from a BIO and parses anddecodes the "name" (e.g. "CERTIFICATE"), any header data and the payload data.If the function succeeds then the "name_out", "header" and "data" arguments arepopulated with pointers to buffers containing the relevant decoded data. Thecaller is responsible for freeing those buffers. It is possible to construct aPEM file that results in 0 bytes of payload data. In this case PEM_read_bio_ex()will return a failure code but will populate the header argument with a pointerto a buffer that has already been freed. If the caller also frees this bufferthen a double free will occur. This will most likely lead to a crash. Thiscould be exploited by an attacker who has the ability to supply malicious PEMfiles for parsing to achieve a denial of service attack.

The functions PEM_read_bio() and PEM_read() are simple wrappers aroundPEM_read_bio_ex() and therefore these functions are also directly affected.

These functions are also called indirectly by a number of other OpenSSLfunctions including PEM_X509_INFO_read_bio_ex() andSSL_CTX_use_serverinfo_file() which are also vulnerable. Some OpenSSL internaluses of these functions are not vulnerable because the caller does not free theheader argument if PEM_read_bio_ex() returns a failure code. These locationsinclude the PEM_read_bio_TYPE() functions as well as the decoders introduced inOpenSSL 3.0.