From: Zooko O'Whielacronx Date: Mon, 12 Sep 2011 22:31:35 +0000 (-0700) Subject: doc: add entry in known_issues.rst about the issue which allows unauthorized deletion... X-Git-Tag: allmydata-tahoe-1.9.0a2~42 X-Git-Url: https://git.rkrishnan.org/pf/content/en/seg/bcase?a=commitdiff_plain;h=48f56dab6fb9cc204ae49392505dcf1c968d2c99;p=tahoe-lafs%2Ftahoe-lafs.git doc: add entry in known_issues.rst about the issue which allows unauthorized deletion of shares ref. #1528 --- diff --git a/docs/known_issues.rst b/docs/known_issues.rst index 27b466ee..cebba4f7 100644 --- a/docs/known_issues.rst +++ b/docs/known_issues.rst @@ -5,6 +5,7 @@ Known Issues * `Overview`_ * `Issues in Tahoe-LAFS v1.8.2, released 2011-01-30` + * `Unauthorized deletion of an immutable file by its storage index`_ * `Potential unauthorized access by JavaScript in unrelated files`_ * `Potential disclosure of file through embedded hyperlinks or JavaScript in that file`_ * `Command-line arguments are leaked to other local users`_ @@ -27,6 +28,85 @@ want to read `the "historical known issues" document Issues in Tahoe-LAFS v1.8.2, released 2011-01-30 ================================================ +Unauthorized deletion of an immutable file by its storage index +--------------------------------------------------------------- + +Due to a flaw in the Tahoe-LAFS storage server software in v1.3.0 through +v1.8.2 a person who knows the "storage index" that identifies an immutable +file can cause the server to delete its shares of that file. + +If an attacker can cause enough shares to be deleted from enough storage +servers, this deletes the file. + +This vulnerability does not enable anyone to read file contents without +authorization (confidentiality), nor to change the contents of a file +(integrity). + +A person could learn the storage index of a file in several ways: + +1. By being granted the authority to read the immutable file—i.e. by being +granted a read capability to the file. They can determine the file's storage +index from its read capability. + +2. By being granted a verify capability to the file. They can determine the +file's storage index from its verify capability. This case probably doesn't +happen often because users typically don't share verify caps. + +3. By operating a storage server, and receiving a request from a client that +has a read cap or a verify cap. If the client attempts to upload, download, +or verify the file with their storage server, even if it doesn't actually +have the file, then they can learn the storage index of the file. + +4. By gaining read access to an existing storage server's local filesystem, +and inspecting the directory structure that it stores its shares in. They can +thus learn the storage indexes of all files that the server is holding at +least one share of. Normally only the operator of an existing storage server +would be able to inspect its local filesystem, so this requires either being +such an operator of an existing storage server, or somehow gaining the +ability to inspect the local filesystem of an existing storage server. + +how to manage it +~~~~~~~~~~~~~~~~ + +Tahoe-LAFS version v1.8.3 or newer (except v1.9a1) no longer has this flaw; +if you upgrade a storage server to a fixed release then that server is no +longer vulnerable to this problem. + +Note that the issue is local to each storage server independently of other +storage servers—when you upgrade a storage server then that particular +storage server can no longer be tricked into deleting its shares of the +target file. + +If you can't immediately upgrade your storage server to a version of +Tahoe-LAFS that eliminates this vulnerability, then you could temporarily +shut down your storage server. This would of course negatively impact +availability—clients would not be able to upload or download shares to that +particular storage server while it was shut down—but it would protect the +shares already stored on that server from being deleted as long as the server +is shut down. + +If the servers that store shares of your file are running a version of +Tahoe-LAFS with this vulnerability, then you should think about whether +someone can learn the storage indexes of your files by one of the methods +described above. A person can not exploit this vulnerability unless they have +received a read cap or verify cap, or they control a storage server that has +been queried about this file by a client that has a read cap or a verify cap. + +Tahoe-LAFS does not currently have a mechanism to limit which storage servers +can connect to your grid, but it does have a way to see which storage servers +have been connected to the grid. The Introducer's front page in the Web User +Interface has a list of all storage servers that the Introducer has ever seen +and the first time and the most recent time that it saw them. Each Tahoe-LAFS +gateway maintains a similar list on its front page in its Web User Interface, +showing all of the storage servers that it learned about from the Introducer, +when it first connected to that storage server, and when it most recently +connected to that storage server. These lists are stored in memory and are +reset to empty when the process is restarted. + +See ticket `#1528 `_ for +technical details. + + Potential unauthorized access by JavaScript in unrelated files --------------------------------------------------------------