VulnerabilityPublished 8 Jul 2025

CVE-2025-53480: Wikimedia Foundation Mediawiki – CheckUser extension · XSS or 'Cross-site Scripting'

Affects Wikimedia Foundation Mediawiki – CheckUser extensionSource CVE Database V5

Not known to be exploited · CVSS 5.4 Medium · fixed in 1.44.0 : update Wikimedia Foundation Mediawiki – CheckUser extension when convenient.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

5.4Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 9% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.44.0, 1.43.0, 1.40.0

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 8 Jul 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Wikimedia Foundation Mediawiki – CheckUser extension to 1.44.0, 1.43.0 or 1.40.0.

Affected software

Product	Affected	Fixed in
Wikimedia Foundation Mediawiki - CheckUser extension	Affected >=1.39.0 <1.40.0 >=1.42.0 <1.43.0 >=1.43.0 <1.44.0	Fixed in 1.40.0 1.43.0 1.44.0

AI-suggested

Immediate patching: Upgrade the CheckUser extension to the fixed versions 1.39.13, 1.42.7, or 1.43.2 or later as applicable. This is the most effective mitigation.
Input validation and output encoding: Review and enhance the handling of internationalized messages and user-supplied parameters to ensure proper escaping and sanitization before rendering in the UI.
Restrict access: Limit access to the Special:Investigate page and the CheckUser extension features to trusted administrators only, reducing the attack surface.
User awareness: Educate users with privileges about the risks of clicking suspicious links, especially those containing unusual query parameters like ?uselang=x-xss.
Web Application Firewall (WAF): Deploy or update WAF rules to detect and block requests containing suspicious parameters or payloads targeting this vulnerability.
Monitoring and logging: Enable detailed logging of access to the CheckUser extension pages and monitor for unusual or suspicious URL parameters or access patterns.
Content Security Policy (CSP): Implement strict CSP headers to limit the execution of inline scripts and reduce the impact of XSS attacks.
Incident response readiness: Prepare to respond to potential exploitation attempts by having procedures to revoke compromised sessions and credentials promptly.

Description

The CheckUser extension’s Special:Investigate page has a vulnerability in the Account information tab, where specific internationalized messages are rendered without proper escaping. Attackers can exploit this by appending ?uselang=x-xss to the URL, causing reflected XSS when the UI renders affected message keys. This issue affects Mediawiki - CheckUser extension: from 1.39.X before 1.39.13, from 1.42.X before 1.42.7, from 1.43.X before 1.43.2.

Impact

For European organizations using Mediawiki with the CheckUser extension, this vulnerability poses a moderate risk. Mediawiki is widely used in various sectors including education, government, and enterprises for collaborative documentation and knowledge management. Exploitation of this XSS vulnerability could allow attackers to steal session cookies or authentication tokens, leading to unauthorized access or privilege escalation within the wiki environment. This could result in unauthorized data disclosure or modification of sensitive content. Since the vulnerability requires low privileges but user interaction, phishing or social engineering campaigns could be used to lure authorized users into clicking malicious links. The impact on confidentiality and integrity is partial but significant, especially for organizations relying on Mediawiki for sensitive or regulated information. The reflected nature of the XSS means the attack is transient but can be used as a vector for further attacks such as delivering malware or redirecting users to malicious sites. Given the collaborative nature of Mediawiki, compromised accounts could also be used to spread misinformation or disrupt organizational knowledge bases. The vulnerability does not affect availability, so denial of service is not a concern here. Overall, European organizations with public-facing or internal Mediawiki installations that have the vulnerable CheckUser extension versions should consider this a medium priority risk.

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #1OWASP Top 10 A05:2025: Injection (opens in a new tab)
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Implementation · Architecture and Design
Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages.
Architecture and Design · Implementation · Attack Surface Reduction
Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide…
OWASP Cheat Sheets
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Injection Prevention (opens in a new tab)
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
OWASP ASVS 4.0.3
V5.3.3 (opens in a new tab)
V1.5.1 (opens in a new tab)
Attack patterns
XSS Using MIME Type Mismatch (opens in a new tab)
DOM-Based XSS (opens in a new tab)
Reflected XSS (opens in a new tab)
Stored XSS (opens in a new tab)
Cross-Site Scripting (XSS) (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 15 Jul 2025, 21:59 UTC

WeaknessesCWE-79

Technical details

References

Community reviews

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