VulnerabilityPublished 20 Jan 2026

CVE-2026-21663: Revive Adserver · Cross-site Scripting

Affects Revive AdserverSource CVE Database V5

Not known to be exploited · CVSS 6.1 Medium.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.0 base score

6.1Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 9% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
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: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
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 20 Jan 2026
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

Affected software

Product	Affected	Fixed in
ReviveRevive Adserver	Affected >=6 <=6.0.4	Fixed in–

AI-suggested

Restrict administrative access to Revive Adserver interfaces by IP whitelisting or VPN-only access to reduce exposure to malicious URLs.
Implement a Web Application Firewall (WAF) with robust XSS detection and blocking capabilities to filter out malicious payloads targeting banner-acl.php.
Educate administrators and relevant staff about phishing and social engineering risks, emphasizing caution when clicking on unsolicited links.
Monitor web server logs and application logs for suspicious URL patterns or repeated access attempts to banner-acl.php with unusual parameters.
Apply Content Security Policy (CSP) headers to limit the execution of unauthorized scripts in the administrator’s browser context.
Regularly update and patch Revive Adserver as soon as official fixes become available.
Consider isolating the ad server environment from other critical infrastructure to contain potential breaches.
Conduct periodic security assessments and penetration testing focusing on web application vulnerabilities including XSS.

Description

CVE-2026-21663 is a reflected Cross-Site Scripting (XSS) vulnerability in the banner-acl.php script of Revive Adserver version 6. An attacker can craft a malicious URL containing an HTML payload that executes when a logged-in administrator visits it, potentially compromising session integrity and enabling unauthorized actions. The vulnerability requires user interaction (administrator clicking the link) but does not require prior authentication to trigger the malicious payload. The CVSS score is 6.1 (medium severity), reflecting the moderate impact on confidentiality and integrity without affecting availability. No known exploits are currently reported in the wild. European organizations using Revive Adserver version 6 should prioritize patching or mitigating this vulnerability to prevent targeted attacks. Countries with high digital advertising activity and significant use of Revive Adserver, such as Germany, the UK, and France, are more likely to be affected. Mitigation includes restricting administrator access to trusted networks, implementing web application firewalls with XSS protections, and educating administrators about phishing risks.

Impact

For European organizations, this vulnerability could lead to unauthorized access to administrative functions within Revive Adserver, potentially allowing attackers to manipulate ad campaigns, redirect ad traffic, or exfiltrate sensitive data related to advertising operations. This can damage brand reputation, cause financial losses due to fraudulent ad activities, and compromise user privacy. Given the role of ad servers in digital marketing ecosystems, exploitation could also facilitate further attacks such as malware distribution through compromised ads. The requirement for administrator interaction limits widespread automated exploitation but increases the risk of targeted spear-phishing campaigns against marketing or IT staff. Organizations in sectors with heavy reliance on digital advertising, such as media, e-commerce, and telecommunications, are particularly vulnerable. The reflected XSS could also be chained with other vulnerabilities to escalate privileges or persist in the environment. The medium severity rating indicates a moderate but non-trivial risk that should be addressed promptly to avoid exploitation.

Summary

CVE-2026-21663 is a reflected Cross-Site Scripting (XSS) vulnerability identified in the banner-acl.php script of Revive Adserver version 6. This vulnerability arises because the script improperly sanitizes user-supplied input parameters, allowing an attacker to inject malicious HTML or JavaScript code into a URL. When a logged-in administrator clicks on this crafted URL, the malicious script executes in their browser context. This can lead to session hijacking, unauthorized actions performed with administrator privileges, or theft of sensitive information such as authentication tokens. The vulnerability does not require the attacker to be authenticated but does require the administrator to interact with the malicious link, making social engineering a likely attack vector. The CVSS 3.0 score of 6.1 reflects that the attack vector is network-based (AV:N), with low attack complexity (AC:L), no privileges required (PR:N), but user interaction is necessary (UI:R). The scope is changed (S:C) because the vulnerability affects resources beyond the vulnerable component, and the impact is limited to confidentiality and integrity (C:L/I:L) without affecting availability (A:N). No public exploits have been reported yet, but the presence of this vulnerability in a widely used open-source ad serving platform poses a risk to organizations relying on it for digital advertising management. The CWE-79 classification confirms this is a classic reflected XSS issue.

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

hackerone.com/reports/3473696 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 28 Jan 2026, 20:21 UTC

WeaknessesCWE-79

Technical details

References

Community reviews

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