CVE-2026-21623Network attack vector

Stored XSS via unfiltered forum post content

Published Jan 16, 2026 · Updated Jan 16, 2026

Stored XSS in StackIdeas EasyDiscuss 1.0.0 through 5.0.15 allows remote authenticated users to inject scripts through forum posts. The forum-post handler stores user-controlled content without sufficient input filtering, so the content executes in another user's browser when the post is viewed. Posting privileges and a subsequent page view are required; execution occurs in the EasyDiscuss site's browser context.

CVSS severity9.4
Critical
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in StackIdeas EasyDiscuss 1.0.0 through 5.0.15 allows remote authenticated users to inject scripts through forum posts. The forum-post handler stores user-controlled content without sufficient input filtering, so the content executes in another user's browser when the post is viewed. Posting privileges and a subsequent page view are required; execution occurs in the EasyDiscuss site's browser context.

The record

CVE
CVE-2026-21623
Published
Jan 16, 2026
Updated
Jan 16, 2026
Vendor
StackIdeas
Product
EasyDiscuss
Classifications
CWE-79, CAPEC-18, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 16, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=1.0.0-5.0.15

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

StackIdeas · EasyDiscussversion=1.0.0-5.0.15

Published CVSS scores

9.4Joomla! ProjectCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A: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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CAPEC-18XSS Targeting Non-Script Elements
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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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