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

The Joomla third-party-extension disclosure wave this pipeline has been tracking has been a file-upload story: unauthenticated uploads reaching code execution, several of which were weaponised and CISA-KEV-listed within days of disclosure. The batch mySites.guru published between 2026-07-20 and 2026-07-23 adds a different and more direct failure. In Balbooa's Gridbox page builder, "A critical unauthenticated authentication bypass in Gridbox let anyone become a Super User on a Joomla site by setting a single browser cookie" (mySites.guru, 2026-07-20). The extension treats a client-supplied cookie value as proof of identity rather than as an assertion to be validated against server-side session state, so an anonymous requester who places an administrator's username in that cookie is served the site as that administrator — no password, no login form, no pre-existing session. Because a Joomla Super User can edit templates, and templates are PHP, the practical outcome is code execution on the web server from a single unauthenticated request. Gridbox 2.20.1 fixes it; the vulnerable code had shipped since the previous release in October 2025, roughly nine months of exposure.

The rest of the week's batch is the same research campaign continuing on its original axis, with two flaws that matter beyond the site itself. EasyStore for Joomla carried an unauthenticated SQL injection able to read the whole site database (CVE-2026-65761, scored 9.3 by the Joomla CNA) plus an order-forgery flaw (CVE-2026-65759, 8.7) where "An anonymous request to the order-repayment endpoint could mark any order paid with no login, no token, and no contact with any payment gateway" (mySites.guru, 2026-07-23), fixed in 2.0.2. Events Booking exposed invoices containing personal and financial data to anonymous requests that simply walked sequential identifiers, fixed in 5.8.2 (mySites.guru, 2026-07-21). Membership Pro's unauthenticated upload was initially disputed by the vendor — the researcher records that "The vendor called it 'not a critical security issue.' The Joomla CNA disagreed" and it was assigned CVE-2026-62415 at 9.1 critical, fixed in Membership Pro 4.6.2 (mySites.guru, 2026-07-21).

There is no public exploitation signal for any of these: the researcher withholds the exact cookie name, endpoints and proof-of-concept code under a fix-first policy. The reason to act ahead of the routine extension-update cycle is the wave's own track record rather than current telemetry — earlier members of this same disclosure series moved from publication to confirmed in-the-wild exploitation within days once the mechanism became public, and a cookie-forgery bypass is trivially rediscovered by anyone who diffs the 2.20.1 release against its predecessor.

Triage: a cookie-forgery bypass leaves little at the network layer to distinguish it — the request is well-formed and returns HTTP 200. The observable is the mismatch between authentication and privilege: administrative actions in Joomla's action log attributed to a Super User account with no preceding successful login event for that account, and no session-establishment record. Legitimate administrator activity is preceded by an authentication event from a consistent source; forged-cookie access produces privileged actions that appear without one. On sites running affected Gridbox versions, template-file modification timestamps postdating the October 2025 release, with no corresponding administrator login, are the artefacts worth reviewing.