CVE-2026-52881: MantisBT: Reflected XSS in admin/install.php via unescaped printf

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog. That can change quickly after a public write-up; re-check if you are affected.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes mantisbt/mantisbt (Composer (PHP)) <= 2.28.3, fixed in 2.28.4. Check your lockfile, including transitive dependencies.

What it is

From the GitHub advisory

MantisBT 2.28.3 and earlier contains six reflected XSS injection points in /admin/install.php. User-supplied parameters are echoed into HTML without escaping via an unescaped printf format string. No authentication is required.

A Content Security Policy (script-src 'self') prevents inline JavaScript execution, but the CSP is missing a form-action directive, allowing exploitation via credential-phishing form injection and open redirects.

Impact - Credential phishing: Attacker crafts a URL that renders a fake login form on the real MantisBT admin page. Admin credentials are submitted to an attacker-controlled server. - Open redirect: Victim is silently redirected to a phishing or malware site. - UI manipulation: CSS injection can hide legitimate page content and overlay attacker-controlled HTML, enabling social engineering.

Patches - https://github.com/mantisbt/mantisbt/commit/297773fbb238c39a153bd888431b41a176132098

Workarounds Remove the /admin directory, as recommended in the Admin Guide

Weakness type: CWE-79.

Product: mantisbt/mantisbt (Composer (PHP)) · Published: 2026-07-15

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: present (depends on deployment conditions)
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).

Timeline

• 2026-07-15 — GitHub-reviewed advisory GHSA-vcrw-4xvv-jh49 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-vcrw-4xvv-jh49 github.com
2. CVE.org record CVE-2026-52881 cve.org
3. NVD entry CVE-2026-52881 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. mantisbt.org mantisbt.org

Critical Composer (PHP) advisories · Today’s Security Digest