What is CVE-2026-100380?

CVE-2026-100380 is Reflected XSS in Wikibase Special:SetLabel language validation. The supplied enrichment data classifies it as Cross-site Scripting mapped to CWE-79 Cross-site Scripting.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Exploitation is reported, but no independent confirmation is available in the sources we have. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-100380 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

1 public PoC repositories reported; 1 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-100380 using CVSS 5.3, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

mediumCross-site Scriptingpublic exploit

CVE-2026-100380

CVE-2026-100380 — Reflected XSS in Wikibase Special:SetLabel language validation

Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Wikimedia Foundation Mediawiki - Wikibase Extension allows Cross-Site Scripting (XSS). This issue affects Mediawiki - Wikibase Extension: from * before 1.46.1, 1.45.5, 1.43.10.

Published Sep 25, 2026Updated Sep 25, 2026Sources: NVD, Wikimedia Foundation (CNA), GitHub, GitHub Security Advisory

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Reported

not confirmed by CISA

EPSS

Not scored

FIRST has not published a score

Affects

Wikimedia Foundation

Mediawiki - Wikibase Extension

CVSS base

5.3

medium

Remediation

The vendor's own words where we have them.

Upgrade Mediawiki - Wikibase Extension to a fixed release. Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
Wikimedia Foundation	Mediawiki - Wikibase Extension	* to < 1.46.1, 1.45.5, 1.43.10	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack Complexity

Low

Attack Vector

Network

Privileges Req

None

User Interaction

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
5.3	CVSS 4.0	medium	—	—	Wikimedia Foundation (CNA)

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

Weakness & attack patterns

CWE-79Cross-site Scripting

Inferred from the weakness class — not observed against this CVE.

CAPEC-63 · Cross-Site Scripting (XSS)CAPEC-591 · Reflected XSS

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

1 of the 1 sampled are weaponized

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Prioritize edge telemetry for network-reachable Mediawiki - Wikibase Extension.
Monitor for scanner or exploit-pattern traffic after 1 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 5.3 (AV:N)
Sep 25, 2026 · NVD
Initial · CVE published
Sep 25, 2026 · NVD
Added · GHSA-x747-q8hh-wvwc published (medium)
Sep 25, 2026 · GitHub Security Advisory

References

4 on the record

gerrit.wikimedia.org/r/q/I7407f9748d72161ce25ad0ba2446869bb1776857
Vendor Advisory
phabricator.wikimedia.org/T434549
Vendor Advisory
nvd.nist.gov/vuln/detail/CVE-2026-100380
NVD
github.com/advisories/GHSA-x747-q8hh-wvwc
Exploit, Third Party Advisory

Elsewhere on this site

Wikimedia Foundationevery CVE for this vendor
Cross-site Scriptingsame class
CWE-79other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-100380 is Reflected XSS in Wikibase Special:SetLabel language validation, a medium vulnerability affecting Mediawiki - Wikibase Extension from Wikimedia Foundation. The current evidence does not list it in CISA KEV, and the exploit status is: Exploitation is reported, but no independent confirmation is available in the sources we have. Public exploit evidence is: 1 public PoC repositories reported; 1 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 5.3 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.