Double free after calling `PEM_read_bio_ex`

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.

Source published

7 Feb 2023 12:00:00 UTC

Source modified

8 Nov 2023 04:10:48 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

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