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EUVD-2026-330463

fkie_cve-2026-52804

Gogs is an open source self-hosted Git service. Prior to 0.14.3, a repository admin collaborator can escalate their privileges to owner-level access by exploiting an off-by-one error in the ChangeCollaborationAccessMode function. This vulnerability is fixed in 0.14.3.

GHSA-4565-r4x7-hg8j — Gogs Vulnerable to Privilege Escalation via Collaboration Access Mode Validation

Affected: Go: gogs.io/gogs

## Summary

A repository admin collaborator can escalate their privileges to owner-level access by exploiting an off-by-one error in the `ChangeCollaborationAccessMode` function.

## Vulnerable Code

In `internal/database/repo_collaboration.go`, line 129:

```go func (r *Repository) ChangeCollaborationAccessMode(userID int64, mode AccessMode) error { // Discard invalid input if mode <= AccessModeNone || mode > AccessModeOwner { return nil } ```

`AccessModeOwner` has value 4. The check `mode > AccessModeOwner` evaluates to `4 > 4 = false`, allowing `AccessModeOwner` to pass through. The correct check should be `mode >= AccessModeOwner`.

The web route at `internal/route/repo/setting.go:413-416` takes the mode as a raw integer from query parameters:

```go func ChangeCollaborationAccessMode(c *context.Context) { if err := c.Repo.Repository.ChangeCollaborationAccessMode( c.QueryInt64("uid"), database.AccessMode(c.QueryInt("mode"))); err != nil { ```

This allows an admin collaborator to POST `mode=4` and escalate to owner.

## Impact

A repository admin collaborator (AccessModeAdmin = 3) can escalate to owner-level access (AccessModeOwner = 4), gaining the ability to: - **Delete the repository** - **Transfer repository ownership** to another user - **Erase wiki data** - Perform all other owner-only operations

The `access` table is also updated (line 181), so the escalated permissions persist across sessions.

## Contrast

The API route…

WID-SEC-W-2026-2013 — Gogs: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Gogs ausnutzen, um erweiterte Berechtigungen zu erlangen, beliebigen Code auszuführen – sogar mit erweiterten Berechtigungen, was zur vollständigen Kontrolle über das System führen kann –, Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren, Cross-Site-Scripting-Angriffe durchzuführen, Benutzer auf bösartige Websites umzuleiten oder einen Denial-of-Service-Zustand zu verursachen.