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-2021-41773CVSS 10A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions. The fix in Apache HTTP Server 2.4.50 was found to be incomplete, see CVE-2021-42013.
CVE-2021-42013CVSS 10It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.
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-2026-57941CVSS 9.8Use After Free vulnerability in Apache HTTP Server's mod_http2 via shared session->bbtmp re-entrancy This issue affects Apache HTTP Server: from 2.4.0 through 2.4.68.

References

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