Description

Gogs has a Protected Branch Deletion Bypass in Web Interface

Summary

An access control bypass vulnerability in Gogs web interface allows any repository collaborator with Write permissions to delete protected branches (including the default branch) by sending a direct POST request, completely bypassing the branch protection mechanism. This vulnerability enables privilege escalation from Write to Admin level, allowing low-privilege users to perform dangerous operations that should be restricted to administrators only.

Although Git Hook layer correctly prevents protected branch deletion via SSH push, the web interface deletion operation does not trigger Git Hooks, resulting in complete bypass of protection mechanisms.

Details

Affected Component

File: internal/route/repo/branch.go

Function: DeleteBranchPost (lines 110-155)

Route Configuration: internal/cmd/web.go:589

m.Post("/delete/*", reqSignIn, reqRepoWriter, repo.DeleteBranchPost)

Root Cause

The DeleteBranchPost function performs the following checks when deleting a branch:

✅ User authentication (reqSignIn)

✅ Write permission check (reqRepoWriter)

✅ Branch existence verification

✅ CommitID matching (optional parameter)

❌ Missing protected branch check

❌ Missing default branch check

While the UI layer (internal/route/repo/issue.go:646-658) correctly checks protected branch status and hides the delete button, attackers can directly construct POST requests to bypass UI restrictions.

Vulnerable Code

Vulnerable implementation (internal/route/repo/branch.go:110-155):

func DeleteBranchPost(c *context.Context) {
	branchName := c.Params("*")
	commitID := c.Query("commit")

	defer func() {
		redirectTo := c.Query("redirect_to")
		if !tool.IsSameSiteURLPath(redirectTo) {
			redirectTo = c.Repo.RepoLink...
Show more

Correct implementation in Git Hook (internal/cmd/hook.go:122-125):

// check and deletion
if newCommitID == git.EmptyID {
    fail(fmt.Sprintf("Branch '%s' is protected from deletion", branchName), "")
}

Correct UI layer check (internal/route/repo/issue.go:646-658):

protectBranch, err := database.GetProtectBranchOfRepoByName(pull.BaseRepoID, pull.HeadBranch)
if err != nil {
	if !database.IsErrBranchNotExist(err) {
		c.Error(err, "get protect branch of repository by name")
		return
	}
} else {
	branchProtected = protectBranch.Protected...
Show more

PoC

Prerequisites

Have Write permissions to the target repository (collaborator or team member)

Target repository has protected branches configured (e.g., main, master, develop)

Access to Gogs web interface

Send Malicious POST Request

# Directly send DELETE request bypassing UI protection
curl -X POST \
  -b cookies.txt \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -d "_csrf=YOUR_CSRF_TOKEN" \
  "https://gogs.example.com/username/repo/branches/delete/main"

Impact

Bypass branch protection mechanism: The core function of protected branches is to prevent deletion, and this vulnerability completely undermines this mechanism

Delete default branch: Can cause repository to become inaccessible (git clone/pull failures)

Bypass code review: After deleting protected branch, can push new branch bypassing Pull Request requirements

Privilege escalation: Writer permission users can perform operations that should only be allowed for Admins

Mitigation

Aliases

References