CVE-2025-7786: Sir Gnuboard XSS Vulnerability

CVE-2025-7786 Overview

CVE-2025-7786 is a cross-site scripting (XSS) vulnerability [CWE-79] in Gnuboard g6 versions up to 6.0.10. The flaw resides in the Post Reply Handler component, specifically in processing of the /bbs/scrap_popin_update/qa/ endpoint. An authenticated remote attacker can inject script content that executes in a victim's browser session when the crafted post reply is rendered. The exploit has been publicly disclosed, increasing the likelihood of opportunistic abuse against unpatched community boards running g6.

Critical Impact
Successful exploitation enables script execution in the context of visiting users, supporting session token theft, forced actions, and phishing content injection within Gnuboard-hosted boards.

Affected Products

Gnuboard g6 versions up to and including 6.0.10
Deployments exposing the /bbs/scrap_popin_update/qa/ scrap popin update endpoint
Community and forum sites built on the SIR Gnuboard g6 platform

Discovery Timeline

2025-07-18 - CVE-2025-7786 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-7786

Vulnerability Analysis

The vulnerability is a stored or reflected cross-site scripting flaw in the Post Reply Handler of Gnuboard g6. Input submitted to the /bbs/scrap_popin_update/qa/ endpoint is not sufficiently sanitized before being embedded in server responses. When the resulting content is rendered in another user's browser, injected HTML or JavaScript executes in the site's origin. The attack requires network access and low-privileged authentication, and success depends on user interaction with the malicious content.

Root Cause

The root cause is improper neutralization of user-supplied input during web page generation, as classified under CWE-79. The scrap popin update workflow accepts attacker-controlled parameters and reflects them into HTML output without applying context-appropriate encoding. The application lacks a consistent output encoding layer for content flowing through the Post Reply Handler, allowing script tags and event handlers to survive processing.

Attack Vector

An attacker with a low-privileged account on the target Gnuboard site crafts a request to /bbs/scrap_popin_update/qa/ containing malicious JavaScript payloads within reply fields. When a moderator or another authenticated user views the affected board or popin, the payload runs in that user's browser. The attacker can then read cookies not protected by HttpOnly, perform actions on the victim's behalf, or redirect users to attacker-controlled infrastructure. Public disclosure of the issue at GitHub Issue #645 and VulDB entry #316847 provides sufficient detail to construct working payloads.

Detection Methods for CVE-2025-7786

Indicators of Compromise

HTTP POST requests to /bbs/scrap_popin_update/qa/ containing <script>, onerror=, onload=, or javascript: substrings in body parameters
Board posts or reply records in the g6 database containing raw HTML tags in fields expected to hold plain text
Outbound browser requests from authenticated user sessions to unfamiliar external hosts shortly after viewing a Gnuboard reply page

Detection Strategies

Deploy web application firewall rules that inspect requests to Gnuboard /bbs/ endpoints for common XSS payload patterns and encoded variants
Review application access logs for repeated submissions to scrap_popin_update from the same account or IP within short intervals
Enable Content Security Policy (CSP) reporting to capture blocked inline script executions originating from Gnuboard pages

Monitoring Recommendations

Alert on new or modified reply records that contain HTML control characters after decoding, particularly <, >, and = in unexpected fields
Monitor administrator and moderator account sessions for anomalous client-side activity such as unexpected profile changes or password resets
Correlate browser telemetry with server logs to identify users who rendered a payload-carrying page

How to Mitigate CVE-2025-7786

Immediate Actions Required

Upgrade Gnuboard g6 to a release later than 6.0.10 once a fixed version is published by the maintainers
Restrict access to reply and scrap functionality for untrusted accounts until patching is complete
Audit existing posts and replies for previously injected payloads and remove malicious content from the database

Patch Information

No vendor advisory URL is listed in the NVD record at time of writing. Track the upstream project via GitHub Issue #645 for fix commits and release notes. Verify any deployed build against the commit that closes the referenced issue before returning the affected endpoint to normal use.

Workarounds

Place a web application firewall in front of Gnuboard and block requests to /bbs/scrap_popin_update/qa/ containing script tags or JavaScript event handler attributes
Enforce a strict Content Security Policy that disallows inline scripts and restricts script sources to trusted origins
Set the HttpOnly and Secure flags on session cookies to limit the impact of script execution on authenticated sessions

bash

# Configuration example
# Example nginx rule to block obvious XSS payloads to the affected endpoint
location /bbs/scrap_popin_update/qa/ {
    if ($request_body ~* "(<script|onerror=|onload=|javascript:)") {
        return 403;
    }
    proxy_pass http://gnuboard_upstream;
}