high CVSS 7.5

CVE-2025-55753·Apache vulnerability

An integer overflow in the case of failed ACME certificate renewal leads, after a number of failures (~30 days in default configurations), to the backoff timer becoming 0. Attempts to renew the certificate then are repeated without delays until it succeeds. This issue affects Apache HTTP Server: from 2.4.30 before 2.4.66. 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: 2.4.30

Until: 2.4.66

Fixed in: 2.4.66

How to fix this CVE

Upgrade Apache HTTP Server to version 2.4.66 or later to remediate CVE-2025-55753, which addresses an integer overflow flaw in the ACME certificate renewal backoff mechanism. This vulnerability can cause the renewal retry timer to reset to zero after approximately 30 days of failed attempts, resulting in rapid renewal loops that consume resources. Delaying this patch leaves your server vulnerable to potential denial-of-service conditions through certificate renewal exhaustion.

sudo dnf check-update httpd && sudo dnf update httpd

Defensia detects this vulnerability

How to check if you are affected

  1. Run 'apache2ctl -v' (Ubuntu/Debian) or 'httpd -v' (RHEL/CentOS) to check your installed Apache version; versions 2.4.30 through 2.4.65 are vulnerable
  2. Check if ACME certificate management is enabled by inspecting your Apache configuration: 'grep -r "mod_md" /etc/apache2/' or 'grep -r "mod_md" /etc/httpd/' to confirm the ACME module is loaded
  3. Review Apache error logs for repeated certificate renewal failures: 'grep -i "acme.*renewal.*fail" /var/log/apache2/error.log' or equivalent httpd log path, looking for patterns spanning 20+ days
  4. After applying the patch, verify the new version with 'apache2ctl -v' or 'httpd -v' and confirm it reports version 2.4.66 or later

FAQ

What is CVE-2025-55753?

CVE-2025-55753 is an integer overflow bug in Apache's ACME certificate renewal logic that causes the backoff timer to underflow to zero after sustained renewal failures, triggering unthrottled retry attempts that can degrade server performance and consume resources.

Is CVE-2025-55753 being actively exploited?

No, CVE-2025-55753 is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are currently available. However, the vulnerability still poses a risk to unpatched servers using ACME-based certificate management.

What versions of Apache are affected by CVE-2025-55753?

Apache HTTP Server versions 2.4.30 through 2.4.65 are vulnerable; version 2.4.66 and later contain the fix.

How do I check if my server is vulnerable to CVE-2025-55753?

Execute 'apache2ctl -v' (Debian/Ubuntu) or 'httpd -v' (RHEL/CentOS) and check if the version falls within the 2.4.30–2.4.65 range. Additionally, verify that mod_md (ACME module) is enabled with 'apache2ctl -M | grep md' or 'httpd -M | grep md'.

Does Defensia detect CVE-2025-55753?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Apache is installed on a monitored server, CVE-2025-55753 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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