critical CVSS 9.8

CVE-2026-28780·Apache vulnerability

Heap-based Buffer Overflow vulnerability in mod_proxy_ajp of Apache HTTP Server. If mod_proxy_ajp connects to a malicious AJP server this AJP server can send a malicious AJP message back to mod_proxy_ajp and cause it to write 4 attacker controlled bytes after the end of a heap based buffer. This issue affects Apache HTTP Server: through 2.4.66. Users are recommended to upgrade to version 2.4.67, which fixes the issue.

Severity
critical
Software
Apache
Fixed in
2.4.67
Published
2026-05-05

Affected versions

Until: 2.4.67

Fixed in: 2.4.67

How to fix this CVE

Upgrade Apache HTTP Server to version 2.4.67 or later to patch the heap buffer overflow in mod_proxy_ajp. This vulnerability allows a malicious AJP backend server to corrupt heap memory and potentially achieve remote code execution. Apply the update immediately, especially if your Apache instance is configured to proxy requests to untrusted or internet-facing AJP application servers.

sudo dnf update httpd httpd-core

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed Apache version: apache2 -v | grep 'Server version' or httpd -v | grep 'Server version'
  2. Verify if mod_proxy_ajp is enabled: apache2ctl -M | grep proxy_ajp or httpd -M | grep proxy_ajp
  3. Search Apache error logs for AJP connection errors or segmentation faults: sudo grep -i 'ajp\|segfault\|buffer' /var/log/apache2/error.log
  4. Confirm the patch is applied by re-running apache2 -v and verifying the version is 2.4.67 or higher after update

FAQ

What is CVE-2026-28780?

CVE-2026-28780 is a critical heap buffer overflow in Apache's mod_proxy_ajp module that occurs when processing malformed AJP protocol messages from a backend server, allowing an attacker to write arbitrary data to heap memory.

Is CVE-2026-28780 being actively exploited?

No, this vulnerability is not currently listed as actively exploited by CISA, and no public exploits are available. However, the CVSS score of 9.8 indicates critical severity and warrants immediate patching.

What versions of Apache are affected by CVE-2026-28780?

All versions of Apache HTTP Server through 2.4.66 are vulnerable. Version 2.4.67 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-28780?

Run 'apache2 -v' or 'httpd -v' to check your version, and 'apache2ctl -M' or 'httpd -M' to confirm mod_proxy_ajp is loaded. If the version is below 2.4.67 and mod_proxy_ajp is active, your server is vulnerable.

Does Defensia detect CVE-2026-28780?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Apache is installed on a monitored server, CVE-2026-28780 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-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-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-2025-58098CVSS 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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