CVE-2016-7426

NTP en versiones anteriores a 4.2.8p9 limita la clasificación de respuestas recibidas desde las fuentes configuradas cuando la limitación de clasificación para todas las asociaciones está habilitado, lo que permite a atacantes remotos provocar una denegación de servicio (prevenir las respuestas de las fuentes) enviando respuestas con una dirección de origen suplantada.

It was found that when ntp is configured with rate limiting for all associations the limits are also applied to responses received from its configured sources. A remote attacker who knows the sources can cause a denial of service by preventing ntpd from accepting valid responses from its sources.

Multiple vulnerabilities have been discovered in the NTP suite: CVE-2016-9311: Trap crash, Reported by Matthew Van Gundy of Cisco ASIG. CVE-2016-9310: Mode 6 unauthenticated trap information disclosure and DDoS vector. Reported by Matthew Van Gundy of Cisco ASIG. CVE-2016-7427: Broadcast Mode Replay Prevention DoS. Reported by Matthew Van Gundy of Cisco ASIG. CVE-2016-7428: Broadcast Mode Poll Interval Enforcement DoS. Reported by Matthew Van Gundy of Cisco ASIG. CVE-2016-7431: Regression: 010-origin: Zero Origin Timestamp Bypass. Reported by Sharon Goldberg and Aanchal Malhotra of Boston University. CVE-2016-7434: Null pointer dereference in _IO_str_init_static_internal(). Reported by Magnus Stubman. CVE-2016-7426: Client rate limiting and server responses. Reported by Miroslav Lichvar of Red Hat. CVE-2016-7433: Reboot sync calculation problem. Reported independently by Brian Utterback of Oracle, and by Sharon Goldberg and Aanchal Malhotra of Boston University. A remote attacker who can send a specially crafted packet to cause a NULL pointer dereference that will crash ntpd, resulting in a Denial of Service. An exploitable configuration modification vulnerability exists in the control mode (mode 6) functionality of ntpd. If, against long-standing BCP recommendations, "restrict default noquery ..." is not specified, a specially crafted control mode packet can set ntpd traps, providing information disclosure and DDoS amplification, and unset ntpd traps, disabling legitimate monitoring by an attacker from remote. An attacker with access to the NTP broadcast domain can periodically inject specially crafted broadcast mode NTP packets into the broadcast domain which, while being logged by ntpd, can cause ntpd to reject broadcast mode packets from legitimate NTP broadcast servers. An attacker with access to the NTP broadcast domain can send specially crafted broadcast mode NTP packets to the broadcast domain which, while being logged by ntpd, will cause ntpd to reject broadcast mode packets from legitimate NTP broadcast servers. Origin timestamp problems were fixed in ntp 4.2.8p6. However, subsequent timestamp validation checks introduced a regression in the handling of some Zero origin timestamp checks. If ntpd is configured to allow mrulist query requests from a server that sends a crafted malicious packet, ntpd will crash on receipt of that crafted malicious mrulist query packet. An attacker who knows the sources (e.g., from an IPv4 refid in server response) and knows the system is (mis)configured in this way can periodically send packets with spoofed source address to keep the rate limiting activated and prevent ntpd from accepting valid responses from its sources. Ntp Bug 2085 described a condition where the root delay was included twice, causing the jitter value to be higher than expected. Due to a misinterpretation of a small-print variable in The Book, the fix for this problem was incorrect, resulting in a root distance that did not include the peer dispersion. The calculations and formulas have been reviewed and reconciled, and the code has been updated accordingly.