high CVSS 7.4

CVE-2025-49812·Apache vulnerability

In some mod_ssl configurations on Apache HTTP Server versions through to 2.4.63, an HTTP desynchronisation attack allows a man-in-the-middle attacker to hijack an HTTP session via a TLS upgrade. Only configurations using "SSLEngine optional" to enable TLS upgrades are affected. Users are recommended to upgrade to version 2.4.64, which removes support for TLS upgrade.

Severity
high
Software
Apache
Fixed in
2.4.64
Published
2025-07-10

Affected versions

Until: 2.4.64

Fixed in: 2.4.64

How to fix this CVE

Upgrade Apache HTTP Server to version 2.4.64 or later to eliminate support for TLS upgrade functionality. If you are running Apache with SSLEngine optional configuration, this upgrade is critical to prevent HTTP session hijacking through man-in-the-middle attacks. Alternatively, disable the SSLEngine optional directive in your Apache configuration as an immediate workaround.

sudo dnf upgrade httpd

Defensia detects this vulnerability

How to check if you are affected

  1. Run 'apache2ctl -v' or 'httpd -v' to check your installed Apache version; versions below 2.4.64 are vulnerable
  2. Check your Apache configuration files (typically /etc/apache2/mods-enabled/ssl.conf or /etc/httpd/conf.d/ssl.conf) for the presence of 'SSLEngine optional' directive; if found, your server is at risk
  3. Search Apache access and error logs for repeated CONNECT method requests followed by TLS ClientHello messages on non-standard ports, which may indicate exploitation attempts
  4. After upgrading to 2.4.64, verify the version with 'apache2ctl -v' or 'httpd -v' and restart Apache with 'sudo systemctl restart apache2' or 'sudo systemctl restart httpd' to confirm the fix is active

FAQ

What is CVE-2025-49812?

This vulnerability is an HTTP request smuggling weakness in Apache's mod_ssl module that allows attackers to desynchronize the HTTP protocol during TLS upgrade negotiation, potentially hijacking user sessions. It only affects configurations where SSLEngine is set to optional, enabling protocol upgrades.

Is CVE-2025-49812 being actively exploited?

No, CVE-2025-49812 is not currently listed in the CISA Known Exploited Vulnerabilities catalog, and no public exploits have been disclosed.

What versions of Apache are affected by CVE-2025-49812?

Apache HTTP Server versions up to and including 2.4.63 are vulnerable if configured with SSLEngine optional. Version 2.4.64 and later have removed TLS upgrade support entirely.

How do I check if my server is vulnerable to CVE-2025-49812?

Run 'apache2ctl -v' or 'httpd -v' to confirm your version is 2.4.63 or earlier, then inspect your Apache configuration files for 'SSLEngine optional' directives in your SSL module configuration.

Does Defensia detect CVE-2025-49812?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Apache is installed on a monitored server, CVE-2025-49812 will appear in your dashboard with remediation steps.

Related Apache CVEs

CVE-2024-38476CVSS 9.8Vulnerability in core of Apache HTTP Server 2.4.59 and earlier are vulnerably to information disclosure, SSRF or local script execution via backend applications whose response headers are malicious or exploitable. Users are recommended to upgrade to version 2.4.60, which fixes this issue.
CVE-2024-38474CVSS 9.8Substitution encoding issue in mod_rewrite in Apache HTTP Server 2.4.59 and earlier allows attacker to execute scripts in directories permitted by the configuration but not directly reachable by any URL or source disclosure of scripts meant to only to be executed as CGI. Users are recommended to upgrade to version 2.4.60, which fixes this issue. Some RewriteRules that capture and substitute unsafely will now fail unless rewrite flag "UnsafeAllow3F" is specified.
CVE-2024-38475CVSS 9.1Improper escaping of output in mod_rewrite in Apache HTTP Server 2.4.59 and earlier allows an attacker to map URLs to filesystem locations that are permitted to be served by the server but are not intentionally/directly reachable by any URL, resulting in code execution or source code disclosure. Substitutions in server context that use a backreferences or variables as the first segment of the substitution are affected.  Some unsafe RewiteRules will be broken by this change and the rewrite flag "UnsafePrefixStat" can be used to opt back in once ensuring the substitution is appropriately constrained.
CVE-2025-23048CVSS 9.1In some mod_ssl configurations on Apache HTTP Server 2.4.35 through to 2.4.63, an access control bypass by trusted clients is possible using TLS 1.3 session resumption. Configurations are affected when mod_ssl is configured for multiple virtual hosts, with each restricted to a different set of trusted client certificates (for example with a different SSLCACertificateFile/Path setting). In such a case, a client trusted to access one virtual host may be able to access another virtual host, if SSLStrictSNIVHostCheck is not enabled in either virtual host.
CVE-2025-58098CVSS 8.3Apache HTTP Server 2.4.65 and earlier with Server Side Includes (SSI) enabled and mod_cgid (but not mod_cgi) passes the shell-escaped query string to #exec cmd="..." directives. This issue affects Apache HTTP Server before 2.4.66. Users are recommended to upgrade to version 2.4.66, which fixes the issue.

References

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