Red Hat Bugzilla – Bug 1201792
CVE-2015-0261 tcpdump: IPv6 mobility printer mobility_opt_print() typecastimg/signedness error
Last modified: 2017-08-01 08:14:16 EDT
A flaw was found in tcpdump's IPv6 mobility printer. A remote attacker could use this flaw to cause tcpdump to crash, resulting in a denial of service, or possibly execute arbitrary code. Upstream patch: http://www.ca.tcpdump.org/cve/0003-test-case-for-cve2015-0261-corrupted-IPv6-mobility-h.patch
Created tcpdump tracking bugs for this issue: Affects: fedora-all [bug 1201799]
The root of this problem is a typcasting/signedness issue introduced by the following commit https://github.com/the-tcpdump-group/tcpdump/commit/57c538422b7fcde95be3df88912f13a792ce7ccc Previously, mobility_opt_print() would handle "len" as "int" (=positive and negative numbers), the commit changed this to "unsigned int" (=only positive numbers). In order to understand why this caused a problem, we need to look at the buffer length check and loop a bit further down in the function: >> for (i = 0; i < len; i += optlen) { >> if (bp[i] == IP6MOPT_PAD1) In the older version, when calling mobility_opt_print() with a negative "len", the "i < len" check would not be satisfied and we would not enter the loop and try to read from bp[i]. In the new version, the previously negative "len" would now be casted to "unsigned int", and will be turned into a (possibly large) positive number instead. Thus, this will mess up the "i < len" check and we incorrectly enter the loop and e.g. try to read from bp[i], where position "i" may now be out of the bounds of "bp". I guess in most scenarios, this will crash due to the out-of-bounds read. If, however, you manage to somehow get around this, it may be possible to corrupt memory further down the code path - although I have not checked in depth how likely this is.
tcpdump-4.7.3-1.fc21 has been pushed to the Fedora 21 stable repository. If problems still persist, please make note of it in this bug report.
tcpdump-4.7.3-1.fc22 has been pushed to the Fedora 22 stable repository. If problems still persist, please make note of it in this bug report.
tcpdump-4.5.1-4.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.
This issue has been addressed in the following products: Red Hat Enterprise Linux 7 Via RHSA-2017:1871 https://access.redhat.com/errata/RHSA-2017:1871