CVE-2026-58269 Overview
CVE-2026-58269 is a two-factor authentication (2FA) bypass in Sync-in Server, an open-source platform for file storage, sharing, collaboration, and syncing. The flaw exists in versions prior to 2.4.0. The POST /api/auth/token endpoint authenticates users with only a username and password, then calls getTokens() to issue full access and refresh JSON Web Tokens (JWTs). The endpoint never checks whether the account has Time-based One-Time Password (TOTP) 2FA enabled. An attacker holding stolen or phished credentials can bypass 2FA in a single request. The parallel POST /api/auth/login endpoint correctly enforces 2FA via setCookies(user, res, true), which gates on user.twoFaEnabled. This is classified under [CWE-288] (Authentication Bypass Using an Alternate Path or Channel).
Critical Impact
Attackers with valid credentials can obtain authenticated JWTs without satisfying TOTP 2FA, defeating a key compensating control against credential theft.
Affected Products
- Sync-in Server versions prior to 2.4.0
- Deployments with TOTP 2FA enabled on user accounts
- Any integration relying on the /api/auth/token endpoint for authentication
Discovery Timeline
- 2026-09-21 - CVE-2026-58269 published to the National Vulnerability Database (NVD)
- 2026-09-21 - Last updated in NVD database
Technical Details for CVE-2026-58269
Vulnerability Analysis
Sync-in Server exposes two authentication entry points that share credential verification but diverge on enforcement of the second factor. The POST /api/auth/login endpoint validates the password and then invokes setCookies(user, res, true), which inspects the user.twoFaEnabled flag and requires a TOTP challenge before issuing session cookies. The POST /api/auth/token endpoint verifies the same credentials but immediately calls getTokens() and returns access and refresh JWTs. The 2FA check is absent from this code path.
An attacker with a valid username and password submits a single HTTP request to /api/auth/token and receives tokens that grant full API access. The tokens are indistinguishable from those issued after a successful 2FA challenge on the login endpoint. This allows credential-theft outcomes such as phishing, password reuse, or infostealer log purchases to escalate directly to account takeover.
Root Cause
The root cause is inconsistent enforcement of authentication policy across parallel endpoints. The token endpoint omits the user.twoFaEnabled gate that the login endpoint applies. This is an authentication bypass through an alternate path, matching [CWE-288]. The design assumes both endpoints share the same security posture, but the token issuance path skips the second-factor step.
Attack Vector
Exploitation requires network access to the Sync-in Server API and valid user credentials. The attacker sends a POST request to /api/auth/token containing the username and password. The server responds with access and refresh JWTs. The attacker then uses these tokens to interact with the API as the compromised user, including reading files, modifying shares, and syncing content. See the GitHub Security Advisory GHSA-92cr-jxw4-5wjg for reference.
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Stop Identity AttacksDetection Methods for CVE-2026-58269
Indicators of Compromise
- Successful POST /api/auth/token responses for accounts where twoFaEnabled is true
- Access token issuance without a corresponding TOTP verification event in application logs
- Authentication events from unfamiliar IP addresses, autonomous systems, or geographies for 2FA-enrolled users
- Refresh token usage patterns diverging from historical login endpoint activity
Detection Strategies
- Correlate token issuance logs from /api/auth/token with the twoFaEnabled attribute for each user account
- Alert when accounts enrolled in TOTP receive JWTs from the token endpoint without a preceding TOTP challenge log entry
- Compare authentication volume between /api/auth/login and /api/auth/token to surface unusual shifts toward the token path
Monitoring Recommendations
- Ingest Sync-in Server authentication and API access logs into a centralized SIEM for correlation with identity telemetry
- Track failed-then-successful credential patterns that indicate credential stuffing followed by token endpoint abuse
- Monitor for JWT reuse from multiple source IPs within short time windows
How to Mitigate CVE-2026-58269
Immediate Actions Required
- Upgrade Sync-in Server to version 2.4.0 or later, which enforces 2FA on the token endpoint
- Rotate JWT signing secrets and invalidate outstanding refresh tokens after upgrading
- Force password resets for high-value accounts and any accounts with suspicious token issuance activity
- Review authentication logs for prior use of /api/auth/token against 2FA-enrolled accounts
Patch Information
Sync-in Server version 2.4.0 patches the issue by enforcing the user.twoFaEnabled check in the token issuance path. Details are published in the GitHub Security Advisory GHSA-92cr-jxw4-5wjg.
Workarounds
- Restrict network access to /api/auth/token at a reverse proxy or web application firewall until the upgrade is applied
- Temporarily disable the token endpoint if it is not required by client applications
- Enforce IP allow-listing for API clients that must retain access during remediation
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
