Merge pull #1086: add warning about UPnP vulnerability

_alerts/2015-10-12-upnp-vulnerability.md

@@ -0,0 +1,65 @@
+---
+## This file is licensed under the MIT License (MIT) available on
+## http://opensource.org/licenses/MIT.
+
+title: "Vulnerability in UPnP library used by Bitcoin Core"
+shorturl: "upnp-vulnerability"
+active: true
+banner: "WARNING: serious vulnerability in UPnP library used by Bitcoin Core (click here to read)"
+bannerclass: "alert"
+---
+
+## Summary
+
+![Disabling UPnP in the GUI](/img/alerts/disable_upnp.png)
+
+Either
+
+- turn off the checkbox in the GUI under Options → Network → Map port using UPNP (see above)
+- add the line `upnp=0` to your `bitcoin.conf` file
+- add `-upnp=0` to the command line options
+
+Also upgrade to a version of Bitcoin Core at least 0.10.3 or 0.11.1 when they
+are released (the release cycle is in progress). These versions upgrade the
+library to a non-vulnerable version, as well as disable UPnP by default to
+prevent this problem in the future.
+
+## Details
+
+Version before 1.9.20151008 of the miniupnpc library are vulnerable to a buffer
+overflow in the XML parser during initial network discovery. The
+vulnerable code triggers at startup of Bitcoin Core if UPnP is enabled.
+
+Details of the vulnerability can be found here: <http://talosintel.com/reports/TALOS-2015-0035/>
+
+It has been verified that the vulnerability can be used to crash the
+application at startup by running a malicious UPnP server on the local
+network.
+
+To have more connectable nodes, the Bitcoin Core executables distributed by
+bitcoin.org include the miniupnpc library and have always had UPnP
+functionality enabled by default, to forward the P2P port.
+
+This applies to the distributed executables only, not those built from source or
+from distribution provided packages. Self-built executables have UPnP disabled
+by default, unless `--enable-upnp-default` was provided to the configure script.
+
+Releases starting from 0.10.3 and 0.11.1, and the upcoming 0.12.0 will still ship
+with (a patched version) of the library, but no longer enable the functionality by default.
+
+## Mitigation
+
+Bitcoin Core executables are compiled with Address Space Layout Randomization (ASLR),
+Stack Smashing Protection (SSP), and non-executable stack and heap (DEP) enabled. This
+makes it harder to use this vulnerability for remote code execution or private
+key leaks. However, it is still advised to upgrade, or if not possible, disable
+UPnP as soon as possible.
+
+## Manual Port Forwarding
+
+With UPnP turned off, your node will still connect to 8 other peers on
+the Bitcoin network to receive new blocks and transactions.  However, it
+will not accept incomming connections from other peers unless you
+manually enable port forwarding on your router.  If you wish to do
+that---it isn't required---please [follow these
+instructions](/en/full-node#network-configuration).