capnproto/security-advisories/2015-03-05-0-c++-addl-cpu-amplification.md

Problem

CPU usage amplification attack, similar to previous vulnerability 2015-03-02-2.

Discovered by

David Renshaw <david@sandstorm.io>

Announced

2015-03-05

CVE

CVE-2015-2313

Impact

• Remotely cause a peer to execute a tight for loop counting from 0 to 2^29, possibly repeatedly, by sending it a small message. This could enable a DoS attack by consuming CPU resources.

Fixed in

• git commit 80149744bdafa3ad4eedc83f8ab675e27baee868
• release 0.5.1.2:
  • Unix: https://capnproto.org/capnproto-c++-0.5.1.2.tar.gz
  • Windows: https://capnproto.org/capnproto-c++-win32-0.5.1.2.zip
• release 0.4.1.1:
  • Unix: https://capnproto.org/capnproto-c++-0.4.1.2.tar.gz
• release 0.6 (future)

Details

Advisory 2015-03-02-2 described a bug allowing a remote attacker to consume excessive CPU time or other resources using a specially-crafted message. The present advisory is simply another case of the same bug which was initially missed.

The new case occurs only if the application invokes the totalSize() method on an object reader.

The new case is somewhat less severe, in that it only spins in a tight for loop that doesn't call any application code. Only CPU time is possibly consumed, not RAM or other resources. However, it is still possible to create significant delays for the receiver with a specially-crafted message.

Preventative measures

Our fuzz test actually covered this case, but we didn't notice the problem because the loop actually completes in less than a second. We've added a new test case which is more demanding, and will make sure that when we do extended testing with American Fuzzy Lop, we treat unexpectedly long run times as failures.