This bug was fixed in the package systemd - 229-4ubuntu19
---------------
systemd (229-4ubuntu19) xenial; urgency=medium
* debian/extra/units/systemd-resolved.service.d/resolvconf.conf: partially
revert, by removing ExecStart|StopPost lines, as these are not needed on
xenial and generate warnings in the journal. (LP: #1704677)
systemd (229-4ubuntu18) xenial; urgency=medium
* debian/extra/units/systemd-resolved.service.d/resolvconf.conf: if resolved
is going to be started, make sure this blocks network-online.target.
(LP: #1673860)
* networkd: cherry-pick support for setting bridge port's priority
(LP: #1668347)
* Cherrypick upstream commit to enable system use kernel maximum limit for
RLIMIT_NOFILE isntead of hard-coded (low) limit of 65536. (LP: #1686361)
* Cherrypick upstream patch for platform predictable interface names.
(LP: #1686784)
* resolved: fix null pointer dereference crash (LP: #1621396)
* Cherrypick core/timer downgrade message about random time addition
(LP: #1692136)
* SECURITY UPDATE: Out-of-bounds write in systemd-resolved (LP: #1695546)
- CVE-2017-9445
* Cherry-pick subset of patches to introduce infinity value in logind.conf
for UserTasksMax (LP: #1651518)
-- Dimitri John Ledkov <x...@ubuntu.com> Mon, 17 Jul 2017 17:00:42
+0100
** Changed in: systemd (Ubuntu Xenial)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1695546
Title:
Out of bounds write in resolved with crafted TCP responses
Status in systemd package in Ubuntu:
Fix Released
Status in systemd source package in Xenial:
Fix Released
Status in systemd source package in Yakkety:
Fix Released
Status in systemd source package in Zesty:
Fix Released
Status in systemd source package in Artful:
Fix Released
Bug description:
[Impact]
Certain sizes passed to dns_packet_new can cause it to allocate a buffer
that's too small. A page-aligned number - sizeof(DnsPacket) + sizeof(iphdr) +
sizeof(udphdr) will do this - so, on x86 this will be a page-aligned number -
80. Eg, calling dns_packet_new with a size of 4016 will result in an allocation
of 4096 bytes, but 108 bytes of this are for the DnsPacket struct.
A malicious DNS server can exploit this by responding with a specially
crafted TCP payload to trick systemd-resolved in to allocating a
buffer that's too small, and subsequently write arbitrary data beyond
the end of it.
To demonstrate this you can run the attached python script. This is a
mock DNS server that sends a response where the first two bytes of the
TCP payload specify a size of 4016 (note, this size is picked to
trigger an out of bounds write on x86 - you'll probably need to pick a
different number for x86-64). You'll need to temporarily set your DNS
server to 127.0.0.1.
[Testcase]
Launch the attached script on i386, point resolved at the started dns server,
execute a dns query via resolved observe that it crashes.
Upgrade systemd package and observe that resolved no longer crashes.
[Regression Potential]
Low, resolved is not used by default in xenial. This is a bug fix to
resolved, in case somebody does use resolved in xenial.
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