Description
Mbed TLS before 3.6.4 allows a use-after-free in certain situations of applications that are developed in accordance with the documentation. The function mbedtls_x509_string_to_names() takes a head argument that is documented as an output argument. The documentation does not suggest that the function will free that pointer; however, the function does call mbedtls_asn1_free_named_data_list() on that argument, which performs a deep free(). As a result, application code that uses this function (relying only on documented behavior) is likely to still hold pointers to the memory blocks that were freed, resulting in a high risk of use-after-free or double-free. In particular, the two sample programs x509/cert_write and x509/cert_req are affected (use-after-free if the san string contains more than one DN).
Problem types
Product status
Any version before 3.6.4
References
lists.debian.org/debian-lts-announce/2025/08/msg00025.html
lists.debian.org/debian-lts-announce/2025/08/msg00013.html
mbed-tls.readthedocs.io/...tech-updates/security-advisories/
github.com/...isories/mbedtls-security-advisory-2025-06-7.md