CVE-2025-54571VulnerabilityPublished 5 Aug 2025Updated 3 Nov 2025

CVE-2025-54571: ModSecurity · Unchecked Return Value

Affects ModSecuritySource CVE Database V5

Not known to be exploited · CVSS 6.9 Medium : upgrade to 2.9.12 when convenient.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 4.0 base score

6.9Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 23% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.9.12

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: Low
Vulnerable system integrity: None
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system 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 Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 5 Aug 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 2026-10-25.

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

Upgrade ModSecurity to 2.9.12.

Affected software

Product	Affected	Fixed in
owasp-modsecurity ModSecurity	Affected <2.9.12	Fixed in 2.9.12

AI-suggested

European organizations should immediately upgrade ModSecurity to version 2.9.12 or later to remediate this vulnerability. In addition to patching, organizations should implement strict validation and sanitization of HTTP headers within their WAF configurations to prevent unauthorized header manipulation. Deploy Content Security Policy (CSP) headers to mitigate the impact of potential XSS attacks by restricting script execution sources. Regularly audit and monitor web traffic for anomalies, specifically looking for unusual Content-Type header changes or suspicious payloads. Employ runtime application self-protection (RASP) tools to detect and block exploitation attempts in real time. Conduct security awareness training for developers and administrators to recognize and respond to WAF misconfigurations. Finally, integrate vulnerability scanning and penetration testing focused on header manipulation and XSS vectors into the security lifecycle to proactively identify similar issues.

Description

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. In versions 2.9.11 and below, an attacker can override the HTTP response’s Content-Type, which could lead to several issues depending on the HTTP scenario. For example, we have demonstrated the potential for XSS and arbitrary script source code disclosure in the latest version of mod_security2. This issue is fixed in version 2.9.12.

Impact

For European organizations, this vulnerability poses a significant risk to web application security, especially those relying on ModSecurity as a frontline defense. Successful exploitation could lead to client-side XSS attacks, enabling attackers to steal session tokens, perform unauthorized actions on behalf of users, or disclose sensitive script code. This undermines user trust and may lead to data breaches involving personal or financial information, contravening GDPR requirements. The impact extends to web service availability indirectly, as exploited XSS can facilitate further attacks or cause reputational damage. Organizations in sectors such as finance, healthcare, e-commerce, and government, which heavily depend on secure web applications, are particularly vulnerable. The lack of authentication or user interaction for exploitation increases the threat surface, making automated attacks feasible. Additionally, compromised client browsers can serve as pivot points for broader network intrusions. Therefore, the vulnerability could have cascading effects on confidentiality, integrity, and indirectly on availability of services.

Summary

CVE-2025-54571 is a vulnerability identified in the OWASP ModSecurity web application firewall (WAF) engine, affecting versions 2.9.11 and earlier. ModSecurity is deployed across major web servers including Apache, IIS, and Nginx, serving as a critical security layer for web applications. The vulnerability stems from an unchecked return value in the code handling HTTP response headers, specifically allowing an attacker to override the Content-Type header of HTTP responses. This flaw is categorized under CWE-252, which involves failure to check the return value of a function, leading to improper handling of security-critical operations. By manipulating the Content-Type header, an attacker can induce browsers to interpret responses in unintended ways, enabling cross-site scripting (XSS) attacks or disclosure of arbitrary script source code. These attacks can compromise the confidentiality and integrity of client-side data and potentially lead to further exploitation of the victim’s environment. The vulnerability is remotely exploitable without requiring authentication or user interaction, increasing its risk profile. Although no active exploits have been reported, the issue is addressed in ModSecurity version 2.9.12. The CVSS v4.0 score of 6.9 reflects a medium severity, driven by network attack vector, low complexity, and no privileges or user interaction needed. The scope is local to the client side, affecting the confidentiality of data processed by the browser. This vulnerability highlights the importance of rigorous input validation and error handling in security middleware components.

CWE-252Unchecked Return Value (opens in a new tab)
Base weaknessLikelihood of exploit: LowOWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
The product does not check the return value from a method or function, which can prevent it from detecting unexpected states and conditions.
Implementation
Check the results of all functions that return a value and verify that the value is expected.
Implementation
For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished.
Implementation
Ensure that you account for all possible return values from the function.
OWASP Cheat Sheets
Logging (opens in a new tab)
Error Handling (opens in a new tab)
OWASP ASVS 4.0.3
V11.1.7 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 3 Nov 2025, 20:34 UTC

WeaknessesCWE-252

Technical details

References

Community reviews

Related threats