
Heimdal's ASN.1 compiler generates code that allows specially crafted DER encodings of CHOICEs to invoke the wrong free function on the decoded structure upon decode error. This is known to impact the Heimdal KDC, leading to an invalid free() of an address partly or wholly under the control of the attacker, in turn leading to a potential remote code execution (RCE) vulnerability. This error affects the DER codec for all CHOICE types used in Heimdal, though not all cases will be exploitable. We have not completed a thorough analysis of all the Heimdal components affected, thus the Kerberos client, the X.509 library, and other parts, may be affected as well. This bug has been in Heimdal since 2005. It was first reported by Douglas Bagnall, though it had been found independently by the Heimdal maintainers via fuzzing a few weeks earlier.
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