When the truncated HMAC extension is enabled and CBC is used, sending a malicious application packet can be used to selectively corrupt 6 bytes on the peer's heap, potentially leading to a crash or remote code execution. This can be triggered remotely from either side in both TLS and DTLS.
If the truncated HMAC extension, which can be set by the compile time option MBEDTLS_SSL_TRUNCATED_HMAC in config.h, is disabled when compiling the library, then the vulnerability is not present. The truncated HMAC extension is enabled in the default configuration.
The vulnerability is only present if
* The compile-time option MBEDTLS_SSL_TRUNCATED_HMAC is set in config.h. (It is set by default) AND
* The truncated HMAC extension is explicitly offered by calling mbedtls_ssl_conf_truncated_hmac(). (It is not offered by default)
Affects versions: all versions of Mbed TLS from version 1.3.0 and up, including all 2.1 and later releases
Created mbedtls tracking bugs for this issue:
Affects: epel-all [bug 1544730]
Affects: fedora-all [bug 1544729]
This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.