In Heimdal through 7.4, remote unauthenticated attackers are able to crash the KDC by sending a crafted UDP packet containing empty data fields for client name or realm. The parser would unconditionally dereference NULL pointers in that case, leading to a segmentation fault. This is related to the _kdc_as_rep function in kdc/kerberos5.c and the der_length_visible_string function in lib/asn1/der_length.c.

References

• https://nvd.nist.gov/vuln/detail/CVE-2017-17439
• heimdal/heimdal#353
• heimdal/heimdal@1a6a6e4
• https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=878144
• https://www.debian.org/security/2017/dsa-4055
• http:https://h5l.org/advisories.html?show=2017-12-08
• http:https://www.h5l.org/pipermail/heimdal-announce/2017-December/000008.html
• http:https://www.h5l.org/pipermail/heimdal-discuss/2017-August/000259.html