CVE-2026-61520: Simple Machines Forum SSRF via image proxy

Severity: high (CVSS 7.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-14 · updated 2026-10-29
Weakness: CWE-918

Description

Simple Machines Forum 2.1 prior to commit b4d23df (fixed in 2.1.8) and 3.0 prior to commit 4bf35cf contains a server-side request forgery vulnerability in the image proxy that allows authenticated attackers to trigger internal HTTP requests by embedding 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. Attackers can leverage SMF's automatic HMAC signature generation for any embedded image URL to obtain valid signed proxy requests targeting internal services such as cloud instance metadata endpoints, internal web applications, and container network services.

Affected products

SimpleMachines SMF: from 2.1.0 before 2.1.8; from 3.0.0-alpha.1 through 3.0.0-alpha.4 — fixed in 2.1.8

How to fix

Upgrade to a fixed version: SimpleMachines SMF 2.1.8. Check the vendor advisory for mitigations.

References

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