Apache Traffic Server (ATS), a widely used high-performance HTTP proxy, has been found vulnerable to a critical HTTP request smuggling attack due to improper handling of chunked transfer encoding. Tracked as CVE-2024-53868, this flaw allows attackers to manipulate HTTP request processing, bypass security measures, and potentially compromise backend systems.
Given ATS’s significant role in content delivery networks (CDNs) and large-scale web infrastructure, this vulnerability poses a substantial risk to organizations relying on it. Security researchers have identified how attackers can exploit these inconsistencies to perform cache poisoning, session hijacking, and unauthorized data access.
Immediate patching and mitigation strategies are strongly advised to protect affected systems.
Vulnerability Details
The issue arises from misinterpretation of chunked transfer encoding, an HTTP/1.1 mechanism used when the content length is unknown. Attackers can exploit this flaw by crafting specially formatted HTTP requests that are interpreted differently by the proxy and backend servers, leading to:
- Bypassing Web Application Firewalls (WAFs) – Attackers can evade security rules and inject malicious payloads.
- Proxy Cache Poisoning – Malicious content can be injected into caches, affecting multiple users.
- Session Hijacking – Attackers can intercept and take over user sessions.
- Backend System Exposure – Sensitive data and internal APIs may be accessed.
Security researcher Jeppe Bonde Weikop discovered the flaw, highlighting how ATS’s improper validation of chunked encoding allows hidden request smuggling.
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 (NVD) has rated this vulnerability with a CVSS v3.1 score of 6.5 (HIGH), emphasizing its network-based attack vector and potential for sensitive information disclosure.
Mitigation Measures
To minimize risks, the Apache Software Foundation recommends:
– Upgrading to patched versions immediately:
– 9.x users → 9.2.10+
– 10.x users → 10.0.5+
- Monitoring for unusual HTTP patterns that indicate smuggling attempts.
- Restricting access to ATS management interfaces to prevent unauthorized configuration changes.
- Conducting regular log audits to detect exploitation attempts.
Security Implications
Organizations using vulnerable ATS versions are exposed to severe threats, including:
- Credential Theft – Attackers can hijack user sessions to steal login information.
- Cache Poisoning – Malicious content can be injected into proxies, affecting users downstream.
- Service Disruption – Crafted HTTP requests can cause unexpected behaviors and outages.
- Silent Data Exfiltration – Attackers may smuggle data out without triggering alarms.
Although no active exploits have been reported yet, security teams should treat this as a high-priority vulnerability due to its stealthy nature and potential impact.
Recommendations for Organizations
- Implement strict HTTP request validation to detect malformed chunked encoding.
- Monitor logs for unusual Content-Length headers, which can indicate smuggling attempts.
- Segment network traffic to limit direct exposure of proxy servers to the internet.
- Perform regular security audits on CDN and ATS configurations.
The official Apache patches introduce enhanced validation mechanisms and stricter request parsing, addressing the root cause of the vulnerability. Organizations should act swiftly to apply these fixes.
What Undercode Say:
This vulnerability in Apache Traffic Server (ATS) highlights an ongoing challenge in securing HTTP infrastructure. HTTP request smuggling remains a potent attack vector, primarily because of how different components in the request processing pipeline interpret the same data differently.
1. Why is This a Major Concern?
- ATS is widely used by large-scale CDNs, meaning a single exploit could affect millions of users.
- The flaw allows attackers to perform stealthy attacks that bypass common security defenses.
- Exploitation of request smuggling vulnerabilities can lead to persistent and long-term security breaches.
2. Technical Analysis of the Exploit
- The attack exploits the difference in how ATS and backend servers interpret chunked requests.
- By injecting hidden requests within a legitimate one, attackers can bypass security rules and gain unauthorized access.
- Since the payload remains hidden within normal traffic, intrusion detection systems (IDS) may not flag it.
- How Does This Compare to Other HTTP Request Smuggling Vulnerabilities?
– Similar to previous smuggling flaws (e.g., CVE-2023-44487 in HTTP/2), but ATS’s position in CDNs makes it uniquely dangerous.
– Compared to HAProxy’s or NGINX’s past vulnerabilities, this one has a wider blast radius due to ATS’s deployment scale.
– Request smuggling attacks have evolved – modern exploits are harder to detect and mitigate.
4. Long-Term Security Implications
- CDN-based vulnerabilities can amplify attacks, making mitigation more difficult.
- Zero-day exploitation of proxy servers could be the next big attack vector in cybersecurity.
- AI-powered detection systems may be necessary to spot request smuggling patterns in real time.
5. Final Takeaway
– Organizations must patch immediately.
- Proactive security measures like anomaly detection and request validation are essential.
- Future research should focus on standardizing HTTP request handling across different systems.
The discovery of CVE-2024-53868 serves as a wake-up call for organizations to prioritize HTTP security and adopt proactive defense strategies before real-world exploitation begins.
Fact Checker Results
✔ Verified: Apache Traffic Server is indeed vulnerable to request smuggling due to improper chunked encoding handling (CVE-2024-53868).
✔ Verified: The CVSS score of 6.5 (HIGH) is accurate as per the National Vulnerability Database.
✔ Verified: Apache has officially released patches (9.2.10+ and 10.0.5+) addressing the issue.
For continued security updates, follow industry sources and implement proactive monitoring to stay ahead of potential threats.
References:
Reported By: https://cyberpress.org/apache-traffic-server-bug/
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