[arch-security] [ASA-201601-16] syncthing: information leakage

[Levente Polyak]

Arch Linux Security Advisory ASA-201601-16
==========================================

Severity: High
Date    : 2016-01-17
CVE-ID  : CVE-2015-8618
Package : syncthing
Type    : information leakage
Remote  : Yes
Link    : https://wiki.archlinux.org/index.php/CVE

Summary
=======

The package syncthing before version 0.12.14-2 is vulnerable to
information leakage.

Resolution
==========

Upgrade to 0.12.14-2.

# pacman -Syu "syncthing>=0.12.14-2"

The problem has been fixed upstream in go version 1.5.3.

Workaround
==========

None.

Description
===========

This issue can affect RSA computations in crypto/rsa, which is used by
crypto/tls. TLS servers on 32-bit systems could plausibly leak their RSA
private key due to this issue. Other protocol implementations that
create many RSA signatures could also be impacted in the same way.

Specifically, incorrect results in one part of the RSA Chinese Remainder
computation can cause the result to be incorrect in such a way that it
leaks one of the primes. While RSA blinding should prevent an attacker
from crafting specific inputs that trigger the bug, on 32-bit systems
the bug can be expected to occur at random around one in 2^26 times.
Thus collecting around 64 million signatures (of known data) from an
affected server should be enough to extract the private key used.

On 64-bit systems, the frequency of the bug is so low (less than one in
2^50) that it would be very difficult to exploit. Nonetheless, everyone
is strongly encouraged to upgrade.

Impact
======

A remote unauthenticated attacker can extract a private RSA key by
passively collecting signatures.

References
==========

https://access.redhat.com/security/cve/CVE-2015-8618
https://groups.google.com/forum/#!topic/golang-dev/MEATuOi_ei4
https://lists.archlinux.org/pipermail/arch-security/2016-January/000516.html

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