On Tue, Feb 18, 2020 at 01:02:21PM -0800, Bernard Aboba via Datatracker wrote: > Reviewer: Bernard Aboba > Review result: Ready with Issues > > TSV-ART Review of draft-ietf-6man-icmp-limits > Bernard Aboba > > Result: Ready with Issues > > This document specifies several new ICMPv6 errors that can be sent > when a node discards a packet due to it being unable to process the > necessary protocol headers because of processing constraints or > limits. Reasons include: > > Code (pertinent to this specification) > 1 - Unrecognized Next Header type encountered > TBA - Extension header too big > TBA - Extension header chain too long > TBA - Too many options in extension header > TBA - Option too big > > ICMP Reliability > > Section 5.2 states: > > " ICMP is fundamentally an unreliable protocol and in real deployment > it may consistently fail over some paths. As with any other use of > ICMP, it is assumed that the errors defined in this document are only > best effort to be delivered. No protocol should be implemented that > relies on reliable delivery of ICMP messages. If necessary, > alternative or additional mechanisms may used to augment the > processes used to to deduce the reason that packets are being > discarded. Such alternative mechanisms are out of scope of this > specification." > > [BA] The last sentence is a bit vague. My assumption is that this is > referring to techniques such as are used in Path MTU discovery (e.g. > tweaking of packets so as to determine potential reasons why packets > are being discarded). However, a reference might be helpful. > > Security Concerns > > Pointer field > > In Section 3.1, the description of the Pointer field states: > > " Pointer > Identifies the octet offset within the invoking packet where > the problem occurred. > > The pointer will point beyond the end of the ICMPv6 packet if > the field having a problem is beyond what can fit in the > maximum size of an ICMPv6 error message." > > [BA] I worry about attackers using the Pointer field for > mischief, such as buffer overflows. The draft currently > does not provide advice to implementers about validating > the Pointer field (e.g. checking it against the length of > the offending packet). Do we really need a 32-bit Pointer field? Very reminiscent of heartbleed, even with the note that "The pointer will point beyond the end of the ICMPv6 packet if the field having a problem is beyond what can fit in the maximum size of an ICMPv6 error message." -Ben > Use by attackers > > Section 4.2 states: > > " A host MAY modify its usage of protocol headers in subsequent packets > to avoid repeated occurrences of the same error." > > [BA] While this response is optional, I do worry about the potential for > spoofed ICMP packets to modify the host's security posture. Are there any > types of usage modifications that a host should be particularly wary > of? > > Section 6 states: > > " In some circumstances, the sending of ICMP errors might conceptually > be exploited for denial of service attack or as a means to covertly > deduce processing capabilities of nodes. As such, an implementation > SHOULD allow configurable policy to withhold sending of the ICMP > errors described in this specification in environments where security > of ICMP errors is a concern." > > [BA] This concern seems quite realistic to me, and as a result, it would > not surprise me if implementations either do not send these ICMP errors, > or withhold them by default. Do you have a position on that? > > > > -- > last-call mailing list > last-call@xxxxxxxx > https://www.ietf.org/mailman/listinfo/last-call -- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-call
