CVE-2026-77508 in Weblate
Summary
by MITRE • 08/26/2026
Weblate is a web based localization tool. Prior to 2026.8, an authenticated user can change the account's primary email through PUT or PATCH requests to /api/users/{username}/ without verifying the new address, allowing a later team invitation for that address to be accepted without access to the intended recipient's mailbox. This issue is fixed in version 2026.8.
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Analysis
by VulDB Data Team • 08/26/2026
Weblate serves as a prominent web-based localization platform designed to facilitate collaborative translation efforts across various software projects and open-source communities. The security flaw identified within versions prior to 2026.8 represents a critical authentication bypass mechanism that exploits the application's user account management API endpoints, specifically targeting the PUT or PATCH methods applied to the /api/users/{username}/ resource path. This vulnerability stems from an insufficient validation process where the system permits authenticated users to modify their primary email address without implementing any form of ownership verification for the new target address. In standard security practices, changing a primary contact method should require confirmation via a link sent to the new email or similar proof-of-possession mechanism to ensure that the individual making the change is indeed the legitimate owner of both accounts involved in the transition.
The technical flaw allows an attacker who has obtained valid credentials for any user account on the Weblate instance to seamlessly redirect all future system communications, including critical security alerts and team invitations, to an email address controlled by the attacker or a third party. By manipulating the API directly rather than through the web interface, which might have additional safeguards or rate limiting, the vulnerability bypasses potential UI-based checks that could otherwise alert users to suspicious activity. This lack of verification creates a significant trust boundary violation where the application assumes that any authenticated request originates from the legitimate account holder without verifying their control over the new identity attribute.
The operational impact of this vulnerability is severe within collaborative environments because it facilitates unauthorized access to team resources and project data through social engineering or automated exploitation techniques. Once an attacker successfully changes a victim's primary email address, they can trigger a password reset for that account if such functionality exists, thereby gaining full administrative control over the compromised user profile. More critically in the context of Weblate’s core function, this flaw enables the acceptance of team invitations intended for other users without requiring access to those recipients' mailboxes. An attacker could invite themselves as a collaborator on projects by exploiting the system's trust in the modified email address, effectively bypassing the invitation confirmation process that normally requires clicking a unique link sent to the original recipient. This undermines the integrity of role-based access control and allows for privilege escalation or unauthorized participation in sensitive localization workflows.
From an industry standard perspective, this vulnerability aligns with CWE-280, which describes improper handling of insufficient validation when changing authentication credentials, as well as CWE-640, where weakness in password management mechanisms is exacerbated by the ability to hijack account recovery paths. In terms of attack vectors and tactics, this behavior maps closely to MITRE ATT&CK technique T1539, specifically the Steal Web Session Cookie variant if session tokens are tied to email changes, or more accurately T1078 Valid Accounts combined with T1528 Stolen Application Access Token scenarios where identity manipulation is used to maintain persistence. The flaw essentially allows an attacker to pivot from a low-privileged authenticated state to higher levels of access by manipulating the underlying user identity metadata that governs authorization decisions across the platform.
To mitigate this risk, organizations running Weblate must immediately upgrade to version 2026.8 or later where the validation logic has been corrected to enforce proof-of-possession for email changes. Until an upgrade is feasible, administrators should implement strict API rate limiting and monitor logs for unusual patterns of PUT or PATCH requests targeting user profile endpoints. Additionally, enabling multi-factor authentication can provide a secondary layer of security that may prevent attackers from fully leveraging the compromised credentials even after successfully altering the associated email address. Security teams should also review existing team memberships to ensure no unauthorized entities have been added through exploited invitation flows during the window of vulnerability exposure.