CVE-2013-5704

What it actually does

The mod_headers module fails to apply RequestHeader unset directives when the header appears in the trailer section of a chunked-encoded HTTP request body, allowing the header to reach the backend despite explicit removal rules.

Why it matters to the business

Attackers may bypass configured header-based access or security policies on affected Apache-based deployments, potentially leading to unauthorized request processing; the issue is more than a decade old with moderate exploit probability and low current prevalence outside legacy Bitnami-packaged environments.

How an attack unfolds

An attacker crafts an HTTP request that uses chunked transfer encoding and places a header (such as an authorization or custom security token) inside the trailing headers section after the final chunk; the server processes the trailer without applying the configured unset directive, allowing the header to influence backend authorization decisions.

How to fix it

Upgrade timescaledb (Bitnami) to version 2.5.2 or later, which incorporates the corrected Apache HTTP Server mod_headers behavior; alternatively disable chunked transfer encoding or migrate away from affected legacy Apache versions where feasible.

How to confirm the fix worked

Confirm the installed package version is 2.5.2 or newer; test by replaying a chunked request with a header in the trailer and verifying that the unset directive is now enforced.

Typical attack path

1. Identify a target endpoint protected by RequestHeader unset rules.
2. Send a chunked HTTP request containing the protected header in the trailer portion.
3. Observe successful bypass of the intended header removal and resulting authorization or policy evasion.

How to detect it

Examine web server access and error logs for chunked requests containing trailer headers; look for repeated requests with non-standard trailer usage that coincide with authorization successes or policy violations.

What your security team should do

• Prioritize upgrade of any remaining Bitnami-packaged instances to the fixed release.
• Review RequestHeader configurations and consider alternative controls such as mod_security or application-level header enforcement.
• Monitor EPSS trend and retire any compensating controls once patching is complete.