CVE-2022-4450

The function PEM_read_bio_ex() reads a PEM file from a BIO and parses and

decodes the "name" (e.g. "CERTIFICATE"), any header data and the payload data.

If the function succeeds then the "name_out", "header" and "data" arguments are

populated with pointers to buffers containing the relevant decoded data. The

caller is responsible for freeing those buffers. It is possible to construct a

PEM 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 pointer

to a buffer that has already been freed. If the caller also frees this buffer

then a double free will occur. This will most likely lead to a crash. This

could be exploited by an attacker who has the ability to supply malicious PEM

files for parsing to achieve a denial of service attack.

The functions PEM_read_bio() and PEM_read() are simple wrappers around

PEM_read_bio_ex() and therefore these functions are also directly affected.

These functions are also called indirectly by a number of other OpenSSL

functions including PEM_X509_INFO_read_bio_ex() and

SSL_CTX_use_serverinfo_file() which are also vulnerable. Some OpenSSL internal

uses of these functions are not vulnerable because the caller does not free the

header argument if PEM_read_bio_ex() returns a failure code. These locations

include the PEM_read_bio_TYPE() functions as well as the decoders introduced in

OpenSSL 3.0.

The OpenSSL asn1parse command line application is also impacted by this issue.