HumHub 1.18.4 - Stored XSS in comment-deletion notifications through unescaped administrator reason

published 2026-08-19 2 mo ago modified 2026-10-27 13 d ago also EUVD-2026-62546

cvss: 7.2; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.5%; EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits: 0; none known

HumHub 1.18.4 contains a stored cross-site scripting vulnerability in the comment-deletion notification flow. A Space administrator can delete another user's comment, choose to notify the original author, and place HTML/JavaScript in the deletion reason.

Patch / fix

links 1

github.com/humhub/humhub#8365 pull request

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: total
Assessed: 2 mo ago (2026-08-19)

Exploit prediction

0.47% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

fluidattacks.com https://fluidattacks.com/es/advisories/personajes referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	4.0	7.2	CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N
CNA	4.0	7.2	CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

HumHub HumHub

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

github.com /humhub/humhub/pull/8365
patch
fluidattacks.com /es/advisories/personajes
third-party-advisory, exploit
github.com /humhub/humhub
product

Sources

CVE List CVE-2026-18430
NVD CVE-2026-18430

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary