Title: OpenBSD ICMPV6 Packet Handling Remote Buffer Overflow Vulnerability
Severity: CRITICAL
Description:
OpenBSD is prone to a remote buffer-overflow vulnerability because it fails to bounds-check user-supplied data before copying it into an insufficiently sized buffer.
Specifically, this issue stems from an overflow in the 'mbuf' kernel memory structure when handling fragmented ICMPv6 packets. The 'mbuf' memory structure is a data structure used to store network packets in kernel memory. It contains another memory structure, 'm_ext', that has a variable 'ext_free' which is used as a pointer to a function called when 'mbuf' is freed. An attacker can exploit this issue by overflowing 'mbuf' to overwrite this variable, manipulating the normal flow of execution when the affected memory structure is freed. Other variables contained in the 'm_ext' memory structure, such as 'ext_nextref' and 'ext_prevref', may also be overwritten to cause denial-of-service conditions.
To exploit this issue, an attacker must be able to inject fragmented IPv6 packets on the target system's local network or to route IPV6 packets to a target machine.
Remote attackers can exploit this issue to execute arbitrary code with kernel-level privileges or to crash the affected computer. Successful exploits will result in a complete compromise of vulnerable computers or cause denial-of-service conditions.
Affected Products:
- OpenBSD OpenBSD 3.1
- OpenBSD OpenBSD 3.6
- OpenBSD OpenBSD 3.8
- OpenBSD OpenBSD 3.9
- OpenBSD OpenBSD 4.0
- OpenBSD OpenBSD 4.1
References:
- OpenBSD: OpenBSD Errata Page
- OpenBSD: OpenBSD Homepage
- US-CERT: Vulnerability Note VU#986425
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