Apache Traffic Server Bug Allows Attackers to Smuggle Malicious Requests

Apache Traffic Server (ATS), a high-performance HTTP proxy server used by major CDNs, has been found vulnerable to HTTP request smuggling attacks due to improper handling of chunked transfer encoding (CVE-2024-53868).

This critical flaw allows attackers to inject malicious requests through malformed chunked messages, potentially bypassing security controls and compromising web infrastructure.

Vulnerability Details

The vulnerability stems from inconsistencies in processing chunked message bodies – an HTTP/1.1 mechanism for streaming data when content length is unknown.

Attackers can craft specially formatted requests that:

• Bypass web application firewalls
• Poison proxy server caches
• Hijack user sessions
• Expose backend systems to unauthorized access

Security researcher Jeppe Bonde Weikop discovered that improper validation of chunked encoding in ATS could lead to request interpretation discrepancies between the proxy and backend servers. This enables the “smuggling” of hidden requests through legitimate traffic.

Affected Versions

Branch	Vulnerable Versions	Patched Version
9.x Series	9.0.0 – 9.2.9	9.2.10+
10.x Series	10.0.0 – 10.0.4	10.0.5+

The National Vulnerability Database assigns a CVSS v3.1 score of 6.5 (HIGH), reflecting the attack’s network-based nature and potential for information disclosure.

Mitigation Measures

The Apache Software Foundation recommends:

1. Immediate upgrade to patched versions:

• 9.x users → 9.2.10+
• 10.x users → 10.0.5+

1. Traffic analysis for unusual HTTP patterns
2. Access restrictions to ATS management interfaces
3. Log auditing for exploit attempts

Security Implications

Organizations using vulnerable ATS versions risk:

• Credential theft through session hijacking
• Cache poisoning attacks affecting multiple users
• Service disruption via malformed requests
• Data exfiltration through smuggled payloads

While no active exploits have been reported, the vulnerability’s nature makes detection challenging.

Security teams should prioritize patching due to the potential for silent compromise of web infrastructure.

Recommendations

• Implement strict HTTP validation rules
• Monitor for unusual Content-Length headers
• Use network segmentation for proxy servers
• Schedule regular security audits of CDN configurations

The patches (available through Apache’s official channels) include enhanced validation of chunked encoding and improved request parsing logic.

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