SimpleMachines SMF up to 2.1.7 Attachment Approval AttachmentApprove.php check authorization

Summaryinfo

A vulnerability classified as critical has been found in SimpleMachines SMF up to 2.1.7. The affected element is the function check of the file Sources/Actions/AttachmentApprove.php of the component Attachment Approval. The manipulation leads to authorization. This vulnerability is uniquely identified as CVE-2026-39903. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in SimpleMachines SMF up to 2.1.7 and classified as critical. This issue affects the function check of the file Sources/Actions/AttachmentApprove.php of the component Attachment Approval. The manipulation with an unknown input leads to a authorization vulnerability. Using CWE to declare the problem leads to CWE-639. The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

Simple Machines Forum 2.1 prior to 2.1.8 and 3.0 prior to 3.0 Alpha 5 contains an authorization bypass vulnerability in Sources/Actions/AttachmentApprove.php where a single-character operator error causes the permission check to always pass regardless of user permissions. An authenticated low-privileged user can approve, reject, or delete any pending attachments on any board without holding the required approve_posts permission, bypass moderation queues for their own uploads, and enumerate and delete other users' pending attachments.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-39903 since 04/07/2026. The exploitation is known to be easy. The attack may be initiated remotely. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available.

By approaching the search of inurl:Sources/Actions/AttachmentApprove.php it is possible to find vulnerable targets with Google Hacking.

Upgrading to version 2.1.8 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• SimpleMachines

Name

• SMF

Version

• 2.1.0
• 2.1.1
• 2.1.2
• 2.1.3
• 2.1.4
• 2.1.5
• 2.1.6
• 2.1.7

Website

• Product: https://github.com/SimpleMachines/SMF/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion