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Date: Thu, 19 Oct 2017 16:17:57 -0400
From: Rich Felker <dalias@...c.org>
To: oss-security@...ts.openwall.com
Cc: Felix Wilhelm <fwilhelm@...gle.com>, musl@...ts.openwall.com
Subject: CVE request: musl libc 1.1.16 and earlier dns buffer overflow

Felix Wilhelm has discovered a flaw in the dns response parsing for
musl libc 1.1.16 that leads to overflow of a stack-based buffer.
Earlier versions are also affected.

When an application makes a request via getaddrinfo for both IPv4 and
IPv6 results (AF_UNSPEC), an attacker who controls or can spoof the
nameservers configured in resolv.conf can reply to both the A and AAAA
queries with A results. Since A records are smaller than AAAA records,
it's possible to fit more addresses than the precomputed bound, and a
buffer overflow occurs.

Users are advised to upgrade to 1.1.17 or patch; the patch is simple
and should apply cleanly to all recent versions:

https://git.musl-libc.org/cgit/musl/patch/?id=45ca5d3fcb6f874bf5ba55d0e9651cef68515395

Users who cannot patch or upgrade immediately can mitigate the issue
by running a caching nameserver on localhost and pointing resolv.conf
to 127.0.0.1.

Rich

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