CVE-2026-35057Public exploitNetwork attack vector

Stored XSS via structured-text placeholder collision

Published Apr 1, 2026 · Updated Apr 1, 2026

Stored XSS in XenForo before 2.2.19 and 2.3.0 through 2.3.9 allows remote authenticated users to execute script in viewers' browsers. XF\Str\Formatter::linkStructuredTextMentions lets placeholder-shaped control bytes in a mention username collide with auto-linked HTML placeholders, then restores raw anchor markup inside an escaped data-username attribute. Posting privileges are required, and viewing the stored legacy profile-post content executes attacker-controlled script in another user's XenForo session.

CVSS severity5.4
Medium
EPSS probability0.17%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

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Summary

What happened

Stored XSS in XenForo before 2.2.19 and 2.3.0 through 2.3.9 allows remote authenticated users to execute script in viewers' browsers. XF\Str\Formatter::linkStructuredTextMentions lets placeholder-shaped control bytes in a mention username collide with auto-linked HTML placeholders, then restores raw anchor markup inside an escaped data-username attribute. Posting privileges are required, and viewing the stored legacy profile-post content executes attacker-controlled script in another user's XenForo session.

The record

CVE
CVE-2026-35057
Published
Apr 1, 2026
Updated
Apr 1, 2026
Vendor
XenForo Ltd.
Product
XenForo
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 1, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 1, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <2.2.19
  2. Affected versionversion=2.3.0 <2.3.10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

XenForo Ltd. · XenForoversion=0 <2.2.19; version=2.3.0 <2.3.10

Published CVSS scores

6.4VulnCheckCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
5.4NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
5.1VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript/JScript

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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