CVE-2022-4450: Double free after calling PEM_read_bio_ex

OpenSSL is vulnerable to a denial of service, caused by a double-free error related to the improper handling of specific PEM data by the PEMreadbioex() function. By sending specially crafted PEM files for parsing, a remote attacker could exploit this vulnerability to cause the system to crash.

— IBM

The function PEMreadbioex() 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 "nameout", "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 PEMreadbioex() 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 PEMreadbio() and PEMread() are simple wrappers around PEMreadbioex() and therefore these functions are also directly affected.

These functions are also called indirectly by a number of other OpenSSL functions including PEMX509INFOreadbioex() and SSLCTXuseserverinfofile() which are also vulnerable. Some OpenSSL internal uses of these functions are not vulnerable because the caller does not free the header argument if PEMreadbioex() returns a failure code. These locations include the PEMreadbioTYPE() functions as well as the decoders introduced in OpenSSL 3.0.

— GitHub

The function PEMreadbioex() 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 "nameout", "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 PEMreadbioex() 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 PEMreadbio() and PEMread() are simple wrappers around PEMreadbioex() and therefore these functions are also directly affected.

These functions are also called indirectly by a number of other OpenSSL functions including PEMX509INFOreadbioex() and SSLCTXuseserverinfofile() which are also vulnerable. Some OpenSSL internal uses of these functions are not vulnerable because the caller does not free the header argument if PEMreadbioex() returns a failure code. These locations include the PEMreadbioTYPE() functions as well as the decoders introduced in OpenSSL 3.0.

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

— NVD