CVE-2026-18526Public exploitNetwork attack vectorHinoki check available

Stored XSS via unencoded oEmbed URL

Published Aug 19, 2026 · Updated Aug 19, 2026

Stored XSS in HumHub Community Edition 1.18.4 and 1.18.4-pl1 lets remote authenticated users execute JavaScript via a crafted oEmbed post link. UrlOembed::confirmationContent() inserts a URL-derived prefix into the consent prompt without HTML encoding when parse_url() yields no host, and UrlOembed::getOEmbed() then runs that untrusted prompt through its script-reconstruction path, recreating injected script tags with a valid CSP nonce. Exploitation requires an authenticated Space member who can create posts and a second authenticated user to view the post; execution occurs in the viewer's session and can drive same-origin actions or read data visible to that user.

CVSS severity7.4
High
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Stored XSS in HumHub Community Edition 1.18.4 and 1.18.4-pl1 lets remote authenticated users execute JavaScript via a crafted oEmbed post link. UrlOembed::confirmationContent() inserts a URL-derived prefix into the consent prompt without HTML encoding when parse_url() yields no host, and UrlOembed::getOEmbed() then runs that untrusted prompt through its script-reconstruction path, recreating injected script tags with a valid CSP nonce. Exploitation requires an authenticated Space member who can create posts and a second authenticated user to view the post; execution occurs in the viewer's session and can drive same-origin actions or read data visible to that user.

The record

CVE
CVE-2026-18526
Published
Aug 19, 2026
Updated
Aug 19, 2026
Vendor
HumHub GmbH & Co. KG
Product
HumHub
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 19, 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=1.18.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

HumHub GmbH & Co. KG · HumHubversion=1.18.4

Published CVSS scores

7.4Fluid AttacksCVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:H/VI:H/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 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 exploitPublished

Weakness, pattern, technique

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

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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