CVE-2019-0211

Apache HTTP Server is the common “web server” that hosts your website. This bug lets an attacker who already gets code running in a low-privileged part of Apache (like a script running with fewer rights) trick Apache into running completely different code as the main Apache process—often with very high privileges. Think of it like smuggling a dangerous program through a side door and then forcing the house’s master key to open the front door.

This matters if your business runs Apache HTTP Server on a Unix system with Apache 2.4 in the affected range (2.4.17 to 2.4.38) and uses MPM event, worker, or prefork. It’s most relevant when an attacker can run code in a less-privileged child process/thread (for example through server-side scripts). It’s essentially a risk when Apache is reachable to attackers who can get code execution in those script/process contexts (not typically from just visiting a normal page).

This is RED because CISA lists CVE-2019-0211 for required action and there is known exploitation capability in the real world. Attackers can use it to escalate from less-privileged code to full code execution under the main Apache process.

1. Confirm exposure

   • Determine the exact Apache version: run apachectl -v (or httpd -v).
   • Confirm it’s Apache HTTP Server 2.4 and whether you’re in the range 2.4.17–2.4.38.
   • Confirm the platform: this issue is for Unix systems (non-Unix is not affected per the backstop).
   • Confirm Apache is using MPM event, worker, or prefork (most common deployments use one of these; check your Apache configuration if unsure).

2. Apply the fix

   • Upgrade Apache to a fixed release: Apache’s remediation points to Apache 2.4.39 (and later) change notes as the fix vehicle.
   • If you rely on a distribution/package or a bundled product, install the vendor security update that includes the fix (your distro’s Apache updates will reference the appropriate fixed package version).

3. Validate

   • After upgrading, verify the running Apache version is no longer within 2.4.17–2.4.38.
   • Ensure the service has restarted and the new binaries are active.

4. If patching is delayed (temporary risk reduction)

   • Reduce the chance that attackers can reach or execute code in Apache’s less-privileged script/process environment (for example, by limiting who can upload or modify server-side scripts, tightening file permissions, and removing unnecessary server-side interpreters).
   • Remove or disable any unnecessary server-side scripting/interpreter components used by your site where possible, since the described exploitation relies on gaining control in a less-privileged child/script context.
   • Monitor for suspicious activity around web requests that trigger server-side code execution.

5. Reporting timeline

   • KEV (CISA) entry exists for CVE-2019-0211; the listed remediation due date was 2022-05-03.

6. What to monitor

   • Look for signs of unexpected command execution or unusual file/process creation initiated from the web server context.

Severity is high (CWE-416: Use After Free is not applicable here; instead, the flaw is a privilege/context separation break). The described weakness is local privilege escalation through manipulation of Apache’s internal scoreboard when Apache is running MPM event/worker/prefork and code executes in less-privileged child processes/threads. An attacker needs the ability to execute code in that child context (e.g., via server-side scripts), after which they can cause arbitrary code execution with the privileges of the main Apache process (often root).

Exploitation status: CVE-2019-0211 is listed in the CISA KEV set (confirmed real-world exploitation); a public exploit exists, indicating weaponization and practical attackability. The fix is available via Apache 2.4.39 (and corresponding vendor updates).