CVE-2026-43621
HighCVSS 8.1Exploitation Probability (EPSS)
Low risk11th percentile - higher than 11% of all known CVEs
Summary
Simple Machines Forum (SMF) through 2.1.7, fixed in commit 6f0dc61, contains an authorization state-confusion vulnerability in the profile loader that allows authenticated low-privileged users to gain administrator access by supplying multiple values for the user parameter. Attackers can exploit the mismatch between Profile::$member and User::$me->is_owner during sequential profile loading to be treated as the owner of an administrator profile, enabling unauthorized password changes and full account takeover.
Risk Assessment
An authenticated low-privileged user can take over an administrator account, leading to full forum compromise, including access to user data and ability to modify content.
Recommendation
Immediately update SMF to a version containing the fix (commit 6f0dc61) and review logs for potential abuse.
Other vulnerabilities in Simple Machines Forum
See all- CVE-2026-61520High
Simple Machines Forum 2.1 prior to commit 4bf35cf and 3.0 prior to commit b4d23df contains a server-side request forgery (SSRF) vulnerability in the image proxy. Authenticated attackers can embed attacker-controlled URLs in BBCode image tags, which the proxy fetches without validating resolved destination IPs against private address ranges, loopback, or link-local addresses.
- CVE-2026-39903High
In Simple Machines Forum 2.1 prior to commit 7d048f8 and 3.0 prior to commit a7875e8, there is an authorization bypass vulnerability in Sources/Actions/AttachmentApprove.php. A single-character operator error causes the permission check to always pass regardless of user permissions.
Original NVD description (English source)
Simple Machines Forum (SMF) through 2.1.7, fixed in commit 6f0dc61, contains an authorization state-confusion vulnerability in the profile loader that allows authenticated low-privileged users to gain administrator access by supplying multiple values for the user parameter. Attackers can exploit the mismatch between Profile::$member and User::$me->is_owner during sequential profile loading to be treated as the owner of an administrator profile, enabling unauthorized password changes and full account takeover.