Overview
The cybersecurity community is currently addressing an identified vulnerability in the Apache HTTP Server, specifically within versions 2.4.35 through to 2.4.63. This significant vulnerability, tagged as CVE-2025-23048, has a significant impact on the integrity of Apache servers. Particularly, it affects configurations where mod_ssl is used across multiple virtual hosts and each restricted to a different set of trusted client certificates.
This vulnerability matters because, if exploited by a savvy attacker, it can lead to an access control bypass by trusted clients, potentially resulting in system compromise or data leakage. This can have massive repercussions for businesses and organizations relying on Apache servers, especially those dealing with sensitive client data or proprietary information.
Vulnerability Summary
CVE ID: CVE-2025-23048
Severity: Critical (9.1 CVSS score)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: The attacker can bypass access controls, potentially leading to system compromise or data leakage.
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Product | Affected Versions
Apache HTTP Server | 2.4.35 – 2.4.63
How the Exploit Works
The exploit works by leveraging a flaw in the mod_ssl configurations of Apache HTTP Server. If mod_ssl is configured for multiple virtual hosts, restricted to different sets of trusted client certificates, an attacker can bypass the access control. This can occur if a client, deemed trusted for one virtual host, tries to access another virtual host where SSLStrictSNIVHostCheck is not enabled. The result is an unauthorized access control bypass and potential system compromise.
Conceptual Example Code
The following is a conceptual example of how the vulnerability might be exploited:
GET /restricted/resource HTTP/1.1
Host: compromisedvirtualhost.example.com
SSL-Session: Resumed
Cert: TrustedClientCertIn this case, the “TrustedClientCert” that is only supposed to have access to another virtual host is used to gain unauthorized access to a different host. The SSL session is resumed, bypassing the access controls in place.