XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser (CVE-2026-73321) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-73321

XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser

Answer in brief

CVE-2026-73321 records a Unknown severity vulnerability in XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser. The current sources do not mark it as known exploited. The current feed maps XenForo/XenForo (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 8, 2026Updated Sep 8, 2026Source checked Sep 8, 2026First seen by HOL Sep 8, 2026Material review Sep 8, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps XenForo/XenForo (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
XenForo/XenForogeneric	>=0 <2.3.13	2.3.13

Recommended response

Check inventory. Check lockfiles and deployed manifests for XenForo/XenForo.
Review the reported fix. Update XenForo/XenForo to 2.3.13 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 8, 2026

Sources and claim methodology

Upstream source description

XenForo before 2.3.13 contains an uncontrolled recursion vulnerability in the BBCode parser that allows authenticated attackers to cause persistent denial of service by submitting a post with deeply nested BBCode tags. Attackers can craft a single malicious post with sufficient nesting depth to exceed PHP's stack limit, causing fatal errors that repeatedly terminate PHP-FPM workers for all visitors rendering the affected thread.

Quoted source text, attributed separately from HOL analysis.