CVE-2017-15650 in Libc
Summary
by MITRE
musl libc before 1.1.17 has a buffer overflow via crafted DNS replies because dns_parse_callback in network/lookup_name.c does not restrict the number of addresses, and thus an attacker can provide an unexpected number by sending A records in a reply to an AAAA query.
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Analysis
by VulDB Data Team • 05/10/2020
The vulnerability identified as CVE-2017-15650 represents a critical buffer overflow flaw within the musl libc library version 1.1.17 and earlier. This issue stems from improper handling of DNS response parsing where the dns_parse_callback function in network/lookup_name.c fails to enforce limits on the number of IP addresses that can be processed. The flaw specifically manifests when the library encounters DNS replies containing A records in response to AAAA queries, creating a scenario where an attacker can manipulate the response structure to trigger memory corruption. This vulnerability directly impacts the fundamental network resolution capabilities of systems utilizing musl libc, making it particularly dangerous in networked environments where DNS queries are frequently processed.
The technical implementation of this vulnerability resides in the DNS parsing logic where the library assumes a fixed relationship between query types and response formats without validating the actual response content. When an application performs DNS resolution using musl libc, the lookup_name.c component processes DNS responses without enforcing bounds checking on the number of addresses returned. This allows an attacker to craft malicious DNS replies that contain more A records than expected, causing the buffer allocated for address storage to overflow. The flaw operates at the intersection of CWE-121, which addresses stack-based buffer overflow conditions, and CWE-787, concerning out-of-bounds write operations, making it a particularly severe memory corruption vulnerability.
The operational impact of this vulnerability extends beyond simple denial-of-service scenarios to potentially enable remote code execution on affected systems. When exploited, the buffer overflow can corrupt adjacent memory regions, potentially allowing attackers to manipulate program execution flow through stack corruption or heap-based attacks. Systems running applications that rely on musl libc for network resolution are particularly vulnerable, including embedded devices, containers, and any software stack that depends on this lightweight C library for system calls. The attack vector requires only the ability to intercept or spoof DNS responses, making it accessible in man-in-the-middle scenarios or through compromised DNS servers, aligning with ATT&CK technique T1071.004 for application layer protocol traffic manipulation.
Mitigation strategies for CVE-2017-15650 focus primarily on updating to musl libc version 1.1.17 or later, which includes proper bounds checking and address limit enforcement. System administrators should prioritize patching affected systems, particularly those in network-critical environments where DNS resolution is frequent. Additional defensive measures include implementing DNS security extensions such as DNSSEC to prevent response manipulation, deploying network monitoring to detect anomalous DNS traffic patterns, and considering network segmentation to limit the impact of potential exploitation. Organizations should also review their application dependencies to ensure all components are using patched versions of musl libc, as this vulnerability affects the underlying system library rather than individual applications. The vulnerability demonstrates the importance of proper input validation in system libraries and highlights the critical nature of maintaining up-to-date system components in cybersecurity defense strategies.