blog: add post about multisig vulnerability

_posts/2021-12-06-vulnerability-multisig.md

@@ -0,0 +1,63 @@
+---
+layout: post
+title: Vulnerabilities identified in Monero multisignature wallet code
+summary: Some vulnerabilities have been identified in the implementation of Monero multisignature wallets
+tags: [urgent]
+author: binaryFate (Core Team)
+---
+
+{% t global.lang_tag %}
+
+```
+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA256
+
+Dear Monero users and participants of the Monero ecosystem,
+
+Some vulnerabilities have been identified in the implementation of
+Monero multisignature wallets.
+These vulnerabilities do not affect the theory supporting multisigs,
+but affect the current wallet code implementing them.
+
+Initially disclosed and discussed via the vulnerability response
+process*, the discussion has been enlarged to other key developers and
+MRL contributors. We agreed together that a public announcement had to
+be made.
+
+These vulnerabilities affect (i) multisignature wallet creation and
+(ii) multisignature transaction signing.
+They can lead to funds being stolen by one of the signing parties.
+
+Until a fix is released, we strongly recommend not to perform any
+multisignature transaction unless all signing parties can be trusted.
+If all signing parties cannot be trusted, no transaction should be
+attempted. Funds are not at risk if they are not moved and if the
+wallet-creation process was not abused.
+
+A fix is currently being reviewed. At this stage we hope to have a
+pull request ready within a week, together with a more detailed
+description of the issues.
+
+Regards,
+
+binaryFate
+
+
+* https://github.com/monero-project/meta/blob/master/VULNERABILITY_RESPONSE_PROCESS.md
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+-----END PGP SIGNATURE-----
+```