Samba: kpasswd service: kpasswd packet that contains malformed asn.1 might cause the server to access 6 bytes of unallocated memory leading server to crash
An out-of-bounds read flaw was found in Samba's Kerberos Key Distribution Center's (KDC) password change (kpasswd) service. When processing malformed ASN.1-encoded Kerberos password change request, Samba server miscalculates the structure size and attempts to read up to six bytes beyond the end of the allocated buffer. While this out-of-bounds read typically results in a harmless decryption failure, if the read hits unmapped memory, it causes the KDC process to crash. An authenticated attacker can send a specially crafted kpasswd request containing malformed ASN.1 data to trigger the out-of-bounds read, which may cause the KDC process to terminate, resulting in a denial of service.
Administrators who do not require the Kerberos password change service may disable it by setting ```kpasswd port = 0``` in ```/etc/samba/smb.conf```.
Where disabling the service is not practical, rate-limiting access to the kpasswd service may reduce the likelihood of successful exploitation until an updated package can be applied.
Note: Disabling kpasswd port will prevent domain users from changing their Kerberos passwords via the kpasswd protocol until patched.
Exploits
Credits
Red Hat would like to thank Tristan Madani (@TristanInSec) (Talence Security) for reporting this issue.