high CVSS 7.5

CVE-2025-59775·Apache vulnerability

Server-Side Request Forgery (SSRF) vulnerability  in Apache HTTP Server on Windows with AllowEncodedSlashes On and MergeSlashes Off  allows to potentially leak NTLM hashes to a malicious server via SSRF and malicious requests or content Users are recommended to upgrade to version 2.4.66, which fixes the issue.

Severity
high
Software
Apache
Fixed in
2.4.66
Published
2025-12-05

Affected versions

From: 2.4.0

Until: 2.4.66

Fixed in: 2.4.66

How to fix this CVE

Apache HTTP Server versions 2.4.0 through 2.4.65 running on Windows with both AllowEncodedSlashes enabled and MergeSlashes disabled are vulnerable to NTLM hash leakage through crafted requests that trigger unintended backend connections. Immediately upgrade to Apache 2.4.66 or later to patch this configuration-specific SSRF vulnerability. If you cannot update immediately, disable AllowEncodedSlashes or enable MergeSlashes as temporary mitigations while preparing your upgrade.

sudo dnf update httpd

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

GET|POST.*(%2f|%5c|/|\).*(localhost|127\.0\.0\.1|169\.254\.169\.254|internal.*host|\\\\[a-zA-Z0-9.-]+\\[a-zA-Z0-9$_-]+)

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Configure WAF rules to block HTTP requests containing encoded backslashes (%5C) and excessive encoded forward slashes (%2F) in the request path, particularly those targeting private IP ranges or localhost-style addresses. Additionally, reject requests with suspicious UNC path patterns (\\servername\share) encoded in the URL.

How to check if you are affected

  1. Run 'apache2ctl -v' or 'httpd -v' to confirm your current Apache version; any version from 2.4.0 to 2.4.65 is affected
  2. Check your Apache configuration files (typically /etc/apache2/apache2.conf or /etc/httpd/conf/httpd.conf) for 'AllowEncodedSlashes On' combined with 'MergeSlashes Off' to confirm the vulnerable configuration exists
  3. Examine Apache access and error logs for unusual requests containing encoded slashes (e.g., '%2F' or '%5C') targeting internal or unexpected hosts; look for patterns like 'GET /%2f..%2f or POST requests with UNC paths
  4. After updating to 2.4.66, re-run 'apache2ctl -v' or 'httpd -v' to verify the new version is active and restart Apache with 'sudo systemctl restart apache2' or 'sudo systemctl restart httpd' to confirm the update took effect

FAQ

What is CVE-2025-59775?

CVE-2025-59775 is a Server-Side Request Forgery (SSRF) vulnerability in Apache HTTP Server on Windows that allows attackers to craft requests with encoded slashes to bypass path normalization, potentially forcing the server to authenticate to an attacker-controlled host and leak NTLM credentials in the process.

Is CVE-2025-59775 being actively exploited?

No, CVE-2025-59775 is not listed on the CISA Known Exploited Vulnerabilities catalog and no public exploit code is currently available. However, the high CVSS score of 7.5 and the specific nature of the attack warrant prompt patching.

What versions of Apache are affected by CVE-2025-59775?

Apache HTTP Server versions 2.4.0 through 2.4.65 are vulnerable when running on Windows with AllowEncodedSlashes set to On and MergeSlashes set to Off. Version 2.4.66 and later patch this issue.

How do I check if my server is vulnerable to CVE-2025-59775?

Run 'httpd -v' or 'apache2ctl -v' to get your version number (if 2.4.0–2.4.65 on Windows, you are affected), then check your Apache configuration with 'grep -i 'AllowEncodedSlashes\|MergeSlashes' /etc/apache2/apache2.conf /etc/apache2/mods-enabled/*.conf' or equivalent paths to confirm the risky configuration combination.

Does Defensia detect CVE-2025-59775?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Apache is installed on a monitored server, CVE-2025-59775 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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