CVE-2026-21640VulnerabilityPublished 20 Jan 2026

CVE-2026-21640: Revive Adserver · Vulnerability

Affects Revive AdserverSource CVE Database V5

Not known to be exploited · CVSS 2.7 Low.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.0 base score

2.7Low

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 16% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

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

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: High: The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to 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 2026-10-26.

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 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–
Packagistrevive/revive-adserver`pkg:composer/revive/revive-adserver`Other threats	Affected =6	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

1. Apply any available patches or updates from Revive that address this vulnerability as soon as they are released. 2. In the absence of patches, restrict administrative access to trusted personnel only and enforce strong authentication mechanisms to reduce the risk of privilege abuse. 3. Sanitize and validate all input fields in the admin settings to prevent injection of malicious format strings. 4. Implement monitoring and alerting for admin console errors or crashes to detect exploitation attempts early. 5. Maintain regular backups of configuration settings to enable quick restoration if the admin console becomes disabled. 6. Consider isolating the ad server environment and limiting network access to reduce exposure. 7. Educate administrators about the vulnerability and safe configuration practices to avoid triggering the issue inadvertently.

Description

HackerOne community member Faraz Ahmed (PakCyberbot) has reported a format string injection in the Revive Adserver settings. When specific character combinations are used in a setting, the admin user console could be disabled due to a fatal PHP error.

Impact

For European organizations, the primary impact is operational disruption of digital advertising management due to the admin console becoming inaccessible. This can delay campaign adjustments, reporting, and revenue-related activities dependent on ad serving. While the vulnerability does not expose sensitive data or allow unauthorized data modification, the loss of admin access can degrade service availability and responsiveness. Organizations heavily reliant on Revive Adserver for advertising, especially those with large-scale or time-sensitive campaigns, may experience business impact from downtime. The threat is limited to administrators, so insider threats or compromised admin accounts pose the greatest risk. Given the low severity and no known active exploitation, the immediate risk is moderate but should not be ignored. Maintaining availability of ad management tools is critical for marketing operations across sectors such as media, e-commerce, and digital agencies in Europe.

CWE-134Use of Externally-Controlled Format String (opens in a new tab)
Base weaknessLikelihood of exploit: High
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
Requirements
Choose a language that is not subject to this flaw.
Implementation
Ensure that all format string functions are passed a static string which cannot be controlled by the user, and that the proper number of arguments are always sent to that function as well. If at all possible, use functions that do not support the %n operator in format strings.
Build and Compilation
Run compilers and linkers with high warning levels, since they may detect incorrect usage.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V5.4.2 (opens in a new tab)
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
Attack patterns
Format String Injection (opens in a new tab)
String Format Overflow in syslog() (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

hackerone.com/reports/3445332 (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

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

WeaknessesCWE-134

Technical details

References

Community reviews

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