Gogs Allows Cross-Repository Comment Deletion via DeleteComment
# IDOR: Cross-Repository Comment Deletion via DeleteComment
Summary
The POST /:owner/:repo/issues/comments/:id/delete endpoint does not verify that the comment belongs to the repository specified in the URL. This allows a repository administrator to delete comments from any other repository by supplying arbitrary comment IDs, bypassing authorization controls.
Vulnerability Details
| Field | Value |
|-------|-------|
| Affected File | internal/route/repo/issue.go |
| Affected Function | DeleteComment (lines 955-968) |
| Secondary File | internal/database/comment.go |
| Secondary Function | DeleteCommentByID (lines 505-520) |
Root Cause
The vulnerability exists due to insufficient authorization validation in the comment deletion flow:
1. Missing Repository Ownership Check in DeleteComment
In internal/route/repo/issue.go, the function retrieves a comment by ID without verifying repository ownership:
```go
func DeleteComment(c *context.Context) {
comment, err := database.GetCommentByID(c.ParamsInt64(":id"))
if err != nil {
c.NotFoundOrError(err, "get comment by ID")
return
}
// Only checks if user is comment poster OR admin of the CURRENT repo (from URL)
if c.UserID() != comment.PosterID && !c.Repo.IsAdmin() {
c.NotFound()
return
} else if comment.Type != database.CommentTypeComment {
c.Status(http.StatusNoContent)
return
}
// No verification that comment.IssueID belongs to c.Repo.Repository.ID!
if err = database.DeleteCommentByID(c.User, comment.ID); err != nil {
c.Error(err, "delete comment by ID")
return
}
c.Status(http.StatusOK)
}
```
2. Database Layer Performs No Authorization
In internal/database/comment.go, the deletion function performs no repository validation:
```go
func DeleteCommentByID(doer *User, id int64) error {
comment, err := GetCommentByID(id)
if err != nil {
if IsErrCommentNotExist(err) {
return nil
}
return err
}
// Directly deletes without checking repository ownership
sess := x.NewSession()
defer sess.Close()
if err = sess.Begin(); err != nil {
return err
}
if _, err = sess.ID(comment.ID).Delete(new(Comment)); err != nil {
// ...
}
// ...
}
```
Proof of Concept
Prerequisites
1. Two users: Alice (attacker) and Bob (victim)
2. Alice is admin of alice/attacker-repo
3. Bob has created an issue with a comment on bob/victim-repo
4. Attacker needs to obtain the comment ID from victim's repository (e.g., ID: 42)
HTTP Request
```http
POST /alice/attacker-repo/issues/comments/42/delete HTTP/1.1
Host: gogs.example.com
Cookie: i_like_gogs=<alice_session_token>
```
