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authorLibravatar Matt McCutchen <matt@mattmccutchen.net>2016-11-14 13:20:24 -0500
committerLibravatar Junio C Hamano <gitster@pobox.com>2016-11-14 11:23:07 -0800
commit235ec24352e151bed37063a004b9800ee0debd74 (patch)
tree6646f0e70a1cd42276ae6e3e4f863b2097146b69 /Documentation/transfer-data-leaks.txt
parentGit 2.8.4 (diff)
downloadtgif-235ec24352e151bed37063a004b9800ee0debd74.tar.xz
doc: mention transfer data leaks in more places
The "SECURITY" section of the gitnamespaces(7) man page described two ways for a client to steal data from a server that wasn't intended to be shared. Similar attacks can be performed by a server on a client, so adapt the section to cover both directions and add it to the git-fetch(1), git-pull(1), and git-push(1) man pages. Also add references to this section from the documentation of server configuration options that attempt to control data leakage but may not be fully effective. Signed-off-by: Matt McCutchen <matt@mattmccutchen.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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+SECURITY
+--------
+The fetch and push protocols are not designed to prevent one side from
+stealing data from the other repository that was not intended to be
+shared. If you have private data that you need to protect from a malicious
+peer, your best option is to store it in another repository. This applies
+to both clients and servers. In particular, namespaces on a server are not
+effective for read access control; you should only grant read access to a
+namespace to clients that you would trust with read access to the entire
+repository.
+
+The known attack vectors are as follows:
+
+. The victim sends "have" lines advertising the IDs of objects it has that
+ are not explicitly intended to be shared but can be used to optimize the
+ transfer if the peer also has them. The attacker chooses an object ID X
+ to steal and sends a ref to X, but isn't required to send the content of
+ X because the victim already has it. Now the victim believes that the
+ attacker has X, and it sends the content of X back to the attacker
+ later. (This attack is most straightforward for a client to perform on a
+ server, by creating a ref to X in the namespace the client has access
+ to and then fetching it. The most likely way for a server to perform it
+ on a client is to "merge" X into a public branch and hope that the user
+ does additional work on this branch and pushes it back to the server
+ without noticing the merge.)
+
+. As in #1, the attacker chooses an object ID X to steal. The victim sends
+ an object Y that the attacker already has, and the attacker falsely
+ claims to have X and not Y, so the victim sends Y as a delta against X.
+ The delta reveals regions of X that are similar to Y to the attacker.