CVE-2018-20103 in HAProxy
Summary
by MITRE
An issue was discovered in dns.c in HAProxy through 1.8.14. In the case of a compressed pointer, a crafted packet can trigger infinite recursion by making the pointer point to itself, or create a long chain of valid pointers resulting in stack exhaustion.
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Analysis
by VulDB Data Team • 06/18/2023
The vulnerability identified as CVE-2018-20103 represents a critical stack exhaustion issue within HAProxy version 1.8.14 and earlier, specifically affecting the dns.c component responsible for DNS packet processing. This flaw manifests when HAProxy encounters DNS packets containing compressed pointers, which are legitimate DNS compression mechanisms used to reduce packet size by referencing previously transmitted data. The vulnerability stems from insufficient validation of pointer references within the DNS decompression process, creating a potential denial of service condition that can be exploited through carefully crafted malicious DNS packets.
The technical implementation of this vulnerability exploits the fundamental mechanism of DNS pointer compression where a pointer references an offset within the same DNS packet to avoid repeating data. When a maliciously constructed DNS packet contains a pointer that references itself, the decompression routine enters infinite recursion, consuming stack resources until the process crashes or becomes unresponsive. Alternatively, attackers can construct chains of valid pointers that create extended recursion sequences, leading to stack exhaustion without necessarily causing immediate crashes. This behavior directly violates the expected operational constraints of DNS packet processing and demonstrates a failure in input validation and recursive call depth management.
The operational impact of CVE-2018-20103 extends beyond simple service disruption to potentially compromise the entire HAProxy deployment, as the vulnerability affects the core DNS processing functionality that many applications rely upon for name resolution services. Organizations using HAProxy as a load balancer, reverse proxy, or application delivery controller face significant risk of denial of service attacks that can render their services unavailable to legitimate users. The vulnerability is particularly concerning because it can be triggered by passive observation of network traffic, meaning that simply receiving malicious DNS packets can cause the service to become unresponsive, without requiring active exploitation or interaction from the attacker.
Security mitigation strategies for CVE-2018-20103 primarily focus on immediate software updates to HAProxy versions 1.8.15 and later, which contain patches addressing the recursive pointer handling issue. Organizations should also implement network-level controls such as DNS filtering and rate limiting to reduce the impact of malicious DNS traffic, while monitoring for unusual DNS packet patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-674 - Uncontrolled Recursion, which specifically addresses situations where recursive operations lack proper termination conditions, and can be mapped to ATT&CK technique T1499.004 - Endpoint Denial of Service, highlighting the broader threat landscape of denial of service attacks against network infrastructure components. Additionally, implementing proper input validation and stack depth monitoring mechanisms within DNS processing components would provide defense in depth against similar vulnerabilities in other network services.