CVE-2026-61425, Balbooa Gridbox for Joomla: a client-supplied cookie is accepted as proof of identity, giving anonymous Super User access

The earlier entry covered CVE-2026-61425, the Gridbox flaw that accepted a client-supplied cookie as proof of identity, fixed in 2.20.1. Balbooa's response was to commission the same researcher to audit the whole component, and that audit found 23 further vulnerabilities in this one extension (mySites.guru, 2026-07-29). The delta that matters is that 2.20.1 (the version the previous entry pointed operators at) is itself vulnerable to a worse flaw than the one it fixed, and that flaw is being exploited.

CVE-2026-65884 carries a CVSS 4.0 base score of 10.0 for a reason that requires no exploit skill at all: the registration handler adds the usergroup IDs supplied in the request to the default group rather than replacing them, so an anonymous visitor can register an ordinary account and place it directly into an administrator group. The researcher describes the defect precisely: the registration handler "adds the default group to whatever groups the visitor asks for, instead of replacing them," so "anyone can register a normal account and place themselves straight into an administrator group" (mySites.guru, 2026-07-29). CVE-2026-65885, scored 9.4, is an authenticated arbitrary file upload, and it becomes remote code execution when chained with the first because the attacker can create the account the upload requires. Both published records give the affected range as 1.0.0 to 2.20.1 (every version the extension has ever shipped up to the fix) and both are marked with an exploit maturity of attacked and an urgency of red by the Joomla CNA that assigned them (mySites.guru, 2026-07-29).

Exploitation is not an inference. The researcher reports holding server access logs showing the exploitation requests arriving and describes 92 planted administrator accounts on a single connected Joomla site, created in batches from 27 July, with usernames following one generator's pattern of a fixed prefix plus a few hex characters paired to matching webmail addresses (mySites.guru, 2026-07-29). Balbooa's own release page corroborates attack traffic indirectly, referring to a recent increase in automated attacks and telling customers to remove the temporary web-server rules it had advised adding to block attacks against Gridbox endpoints (Balbooa, 2026-07-29).

Getting to a fixed build took three attempts, which is itself operationally relevant for anyone who applied an interim Gridbox update this month. The researcher's account of the coordinated-disclosure process records that the vendor's first proposed fix left several reported findings live, including an anonymous SQL injection returning password hashes that had been patched at only one of several identical reachable entry points, and that the second closed that and the actively-exploited routes but still left a forgeable payment-gateway callback signature and a SQL injection reachable by a low-privilege authenticated user (mySites.guru, 2026-07-29). Only 2.20.2, released 2026-07-29, closes all of it, and the vendor states the build was given to the reporting researcher for independent verification before release (Balbooa, 2026-07-29). The remaining 21 findings are described only by shape, with nine further CVE IDs reserved but unpublished, so the public picture of this component's exposure is not yet complete.

Detection. Both halves of the chain leave records in places most Joomla operators already keep. For the privilege escalation, the artifact is a user account whose administrator-group membership was established at creation time rather than by a later administrative change, visible in the user table and in Joomla's own action logs as a registration event that produced an elevated account, with no corresponding admin action. Cluster it by timing: automated abuse of this flaw produces accounts in batches minutes apart, not the trickle of genuine sign-ups. For the upload half, the signal is a file appearing in a web-reachable directory with a server-executable extension, written by the web server user, followed by requests to that path from a small number of sources, and in web-server access logs, POST requests to the extension's registration and upload endpoints from addresses with no prior browsing history on the site.

Triage: a public Joomla site with open registration collects spam accounts constantly, so a new unrecognised user is not the signal. The discriminator is the group membership: ordinary registration spam lands in the default registered-users group and stays there, while these accounts sit in an administrator group from the moment they were created. Any self-registered account holding administrative rights on a Gridbox site should be treated as planted rather than misconfigured.