CVE-2015-1821 in chrony
Summary
by MITRE
Heap-based buffer overflow in chrony before 1.31.1 allows remote authenticated users to cause a denial of service (chronyd crash) or possibly execute arbitrary code by configuring the (1) NTP or (2) cmdmon access with a subnet size that is indivisible by four and an address with a nonzero bit in the subnet remainder.
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Analysis
by VulDB Data Team • 05/09/2022
The vulnerability CVE-2015-1821 represents a critical heap-based buffer overflow in the chrony time synchronization daemon version 1.31.0 and earlier. This flaw affects the NTP and cmdmon access configuration mechanisms within chrony, creating a remote authenticated attack vector that can lead to either denial of service or arbitrary code execution. The vulnerability specifically targets the handling of network subnet configurations where the subnet size is indivisible by four, combined with an address that contains nonzero bits in the subnet remainder. This particular combination triggers memory corruption during the parsing and processing of these malformed network parameters.
The technical implementation of this vulnerability stems from improper validation of subnet mask calculations within chrony's network configuration handling code. When an authenticated attacker provides a subnet configuration that violates the mathematical requirements for valid subnet masks, the daemon fails to properly bounds-check memory allocations for storing these network parameters. This results in writing data beyond the allocated heap memory boundaries, causing heap corruption that manifests as either program crashes or potential code execution opportunities. The vulnerability is classified as CWE-121 Heap-based Buffer Overflow, which is a well-documented category of memory safety issues in C/C++ applications. The flaw demonstrates poor input validation and memory management practices that are common in network daemon applications where complex network parameters must be processed and validated.
From an operational perspective, this vulnerability creates significant risk for systems relying on chrony for time synchronization services. The remote authenticated nature means that attackers who can establish connections to the chrony daemon with valid credentials can exploit this flaw without requiring local system access. The potential impact includes complete service disruption through daemon crashes, which can cascade into time synchronization failures across networked systems. In environments where precise timekeeping is critical for security operations, such as those utilizing time-based authentication systems, certificate validation, or security event correlation, this vulnerability can severely compromise operational continuity. The possibility of arbitrary code execution adds another dimension of risk, potentially allowing attackers to gain control over the time synchronization server and subsequently compromise other systems within the network that depend on this service.
Mitigation strategies for CVE-2015-1821 should focus on immediate patching of chrony installations to version 1.31.1 or later, which contains the necessary fixes for the buffer overflow conditions. Network administrators should also implement strict access controls to limit who can configure NTP and cmdmon parameters, reducing the attack surface for authenticated exploitation. Monitoring for unusual configuration changes or connection attempts to chrony services can help detect potential exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1190 Exploit Public-Facing Application, highlighting the need for proper network segmentation and access controls. Additional defensive measures include implementing network-based intrusion detection systems that can identify malformed subnet configurations and applying principle of least privilege to chrony configuration access. System hardening techniques such as address space layout randomization and stack canaries should also be considered as additional layers of protection against potential exploitation attempts that could leverage this memory corruption vulnerability.