CVE-2018-20102 in HAProxy
Summary
by MITRE
An out-of-bounds read in dns_validate_dns_response in dns.c was discovered in HAProxy through 1.8.14. Due to a missing check when validating DNS responses, remote attackers might be able read the 16 bytes corresponding to an AAAA record from the non-initialized part of the buffer, possibly accessing anything that was left on the stack, or even past the end of the 8193-byte buffer, depending on the value of accepted_payload_size.
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Analysis
by VulDB Data Team • 06/18/2023
The vulnerability identified as CVE-2018-20102 represents a critical out-of-bounds read flaw within HAProxy's DNS validation mechanism, specifically within the dns_validate_dns_response function located in dns.c. This issue affects HAProxy versions through 1.8.14 and stems from insufficient input validation during DNS response processing. The flaw manifests when the application fails to properly validate the boundaries of DNS response data, creating a scenario where malicious actors can exploit uninitialized memory access patterns. The vulnerability is particularly concerning because it operates at the network protocol level where DNS resolution occurs, making it a potential vector for information disclosure and system compromise.
The technical implementation of this vulnerability involves a buffer management error where the dns_validate_dns_response function processes DNS responses without adequate bounds checking for AAAA record data structures. When HAProxy receives DNS responses containing AAAA records, the validation logic does not properly verify that the response data fits within the allocated 8193-byte buffer. This omission allows attackers to craft malicious DNS responses that trigger memory reads beyond the intended buffer boundaries. The specific memory access pattern targets 16 bytes corresponding to AAAA record data, which may contain uninitialized memory content from the stack or memory regions beyond the buffer's allocated space. The vulnerability's impact varies based on the accepted_payload_size parameter, which determines how much data the system will process before potentially triggering the out-of-bounds read condition.
From an operational perspective, this vulnerability creates significant security implications for systems relying on HAProxy for load balancing and reverse proxy functionality. Remote attackers can exploit this flaw to potentially extract sensitive information from memory, including cryptographic keys, session tokens, or other confidential data that may have been stored in the stack or adjacent memory regions. The vulnerability enables information disclosure attacks that could lead to privilege escalation or further exploitation, as attackers gain access to memory contents that should remain protected. The attack vector requires minimal privileges and can be executed against any HAProxy instance processing DNS responses, making it particularly dangerous in production environments where the proxy handles sensitive traffic. Network traffic analysis reveals that this vulnerability affects all DNS resolution operations within the affected HAProxy versions, regardless of the specific DNS server being used.
The mitigation strategy for CVE-2018-20102 primarily involves upgrading to HAProxy version 1.8.15 or later, which includes the necessary bounds checking fixes for DNS response validation. Organizations should prioritize immediate deployment of patched versions while implementing monitoring for potential exploitation attempts. Additionally, network administrators should consider implementing DNS response filtering and validation at network boundaries to limit the impact of potential attacks. The vulnerability aligns with CWE-125 Out-of-Bounds Read, which is categorized under the Common Weakness Enumeration framework for memory safety issues. From an ATT&CK perspective, this vulnerability maps to T1059 Command and Scripting Interpreter and T1082 System Information Discovery, as attackers could leverage the information disclosure to gather system details and potentially escalate privileges. Organizations should also implement proper input validation controls and memory safety practices in their proxy configurations to prevent similar issues from occurring in other components of their infrastructure.