CVE-2026-100277 in YouTrack
Summary
by MITRE • 09/30/2026
In JetBrains YouTrack before 2026.2.19197 account takeover was possible by replaying a notification signature
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified in JetBrains YouTrack prior to version 2026.2.19197 represents a critical authentication bypass mechanism rooted in the improper validation of cryptographic signatures used for user notifications. This flaw allows an attacker to perform account takeover by exploiting the replayability of notification tokens, which are designed to facilitate secure password resets or email verification processes without requiring full re-authentication through standard login flows. The core technical deficiency lies in the server-side logic that fails to enforce strict uniqueness and expiration constraints on these signature-based authentication tokens. Instead of binding each token to a specific session identifier, IP address, or single-use counter, the system accepts any validly signed notification payload presented within its nominal validity window. This design oversight effectively transforms what should be a one-time authorization mechanism into a reusable credential that can be intercepted and replayed by malicious actors who have gained access to network traffic or compromised user email accounts temporarily.
From an operational perspective, this vulnerability enables attackers to bypass multi-factor authentication controls if the notification flow is configured as part of the secondary verification step. By capturing a legitimate password reset link or verification token sent via email, an attacker can replay this request against the application interface at any point before the token expires. This capability allows for complete account compromise without needing to crack passwords or exploit additional software vulnerabilities in other components. The impact is severe because it undermines the fundamental trust model of identity management systems, where out-of-band notifications are relied upon as a secure channel for sensitive actions. Users whose accounts are targeted may find their data exposed, modified, or deleted by unauthorized parties who have successfully replayed these notification signatures to assume control over the account credentials and associated permissions within the YouTrack instance.
This vulnerability aligns with CWE-294, which describes authentication bypass when capture of a credential is followed by its reuse, specifically in contexts where tokens are not properly invalidated after use or lack sufficient entropy combined with binding mechanisms. Furthermore, it maps to MITRE ATT&CK technique T1078, Valid Accounts, as the attacker leverages legitimate but misused credentials (the notification token) to gain access. The exploitation path typically involves intercepting HTTP traffic containing the signed URL or extracting the signature from email headers if the communication channel is not fully encrypted and authenticated end-to-end. Defenders must recognize that cryptographic signatures alone are insufficient for security; they must be coupled with stateful validation checks such as nonce values, session binding, and immediate invalidation upon first use to prevent replay attacks effectively.
Mitigation strategies require an immediate upgrade to JetBrains YouTrack version 2026.2.19197 or later, where the vendor has addressed this logic flaw by implementing stricter token lifecycle management. Administrators should ensure that all notification tokens are bound to specific user sessions and invalidated immediately after successful authentication or password reset operations. Additionally, enforcing HTTPS for all communication channels reduces the risk of initial interception, although it does not mitigate replay attacks if the server-side validation remains weak. Security teams should also monitor logs for unusual patterns of token usage, such as multiple attempts from different IP addresses within a short timeframe using the same signature, which may indicate active exploitation attempts before patches are applied. Regular audits of authentication flows and adherence to OWASP guidelines on session management will help prevent similar vulnerabilities in future deployments.