Gogs Vulnerable to 2FA Bypass via Recovery Code

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Security Advisory: 2FA Bypass via Recovery Code Vulnerability Type: 2FA Authentication Bypass Affected Software: GOGS Severity: High Date: Aug 5, 2025 Discoverer: OpenAI Security Research Summary Gogs’ 2FA recovery code validation does not scope codes by user, enabling cross-account bypass. If an attacker knows a victim’s username and password, they can use Security Advisory_ 2FA Bypass via Recovery Code - Google Docs.pdf any unused recovery code (e.g., from their own account) to bypass the victim’s 2FA. This enables full account takeover and renders 2FA ineffective in all environments where it's enabled. Affected Versions Software: Gogs Confirmed Version(s): All versions with 2FA support Likely Affected: All versions since introduction of UseRecoveryCode logic Introduced Commit: a617d52374e937db0edacfba2a26bdd14a05538e Commit: a617d52374e937db0edacfba2a26bdd14a05538e Author: Joe Chen Date: Apr 5, 2017 Description: 2fa: initial support

Vulnerability Details The function UseRecoveryCode in internal/database/two_factor.go fails to check that the recovery code belongs to the authenticating user. Instead, it looks for any unused recovery code: Vulnerable Code Snippet

func UseRecoveryCode(_ int64, code string) error {
    recoveryCode := new(TwoFactorRecoveryCode)
    has, err := x.Where("code = ?", code).And("is_used = ?", false).Get(recoveryCode)
    ...
}

Although the caller passes userID, it is ignored. The result is a global lookup for any unused code, allowing an attacker to submit their own recovery code during another user's login flow.

Call Chain

web login handler → UseRecoveryCode(userID, code) → DB query without userID constraint Proof-of-Concept (PoC) Description This bug is tested against the latest version of Gogs hosted on Dockerhub. Attacker uses their own recovery code to bypass another user’s 2FA. Steps Create attacker account A and enable 2FA. Save a code like "abcde-fghij". Obtain credentials for victim B. Attempt login as B via web. When prompted for recovery code, submit A's code. Login as B succeeds; A's code is marked as used.

Impact 2FA rendered ineffective for all users Realistic Exploitation Scenarios Public Gogs instances with 2FA enabled Developer or maintainer accounts Enterprise self-hosted Gogs servers Potential Impact This vulnerability critically undermines 2FA. Since recovery codes are not globally unique and lack user scoping, any attacker with victim credentials can use one of their own recovery codes to complete login as the victim — bypassing all 2FA protections. This opens the door to account hijacking, data exfiltration, and downstream supply chain compromise. Timeline August 2025: Discovered via GPT5 August 2025: Reproduced and confirmed via PoC and sanitizer Aug 6, 2025 - Sent to Gogs via