Overview
The vulnerability CVE-2025-49812 is a critical flaw in Apache HTTP Server that could allow an attacker to hijack an HTTP session via a TLS upgrade. This vulnerability could potentially lead to system compromise or data leakage, affecting users running versions of Apache HTTP Server up to 2.4.63. Due to the severity of this vulnerability, it is essential for affected users to understand the risks and apply appropriate mitigations.
Vulnerability Summary
CVE ID: CVE-2025-49812
Severity: High (CVSS: 7.4)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: System compromise or data leakage if successfully exploited
Affected Products
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Product | Affected Versions
Apache HTTP Server | Up to 2.4.63
How the Exploit Works
The vulnerability lies in the mod_ssl configurations of Apache HTTP Server. In certain configurations where “SSLEngine optional” is used to enable TLS upgrades, an attacker can exploit this vulnerability to desynchronise HTTP requests. This desynchronisation attack allows a malicious actor to hijack an HTTP session, paving the way for a man-in-the-middle attack. This could lead to potential system compromise or data leakage.
Conceptual Example Code
A conceptual example of how the vulnerability might be exploited could involve a malicious actor sending a specially crafted HTTP request to the vulnerable server. The request could force the server to upgrade the connection to TLS, allowing the attacker to hijack the HTTP session. An example of such a request might look like this:
GET / HTTP/1.1
Host: vulnerable-server.com
Upgrade: TLS/1.2
Connection: Upgrade
Upon receiving such a request, a vulnerable server might upgrade the connection to TLS, leaving the session open to hijacking by the attacker.
