CVE-2017-16548 in rsync
Summary
by MITRE
The receive_xattr function in xattrs.c in rsync 3.1.2 and 3.1.3-development does not check for a trailing '\0' character in an xattr name, which allows remote attackers to cause a denial of service (heap-based buffer over-read and application crash) or possibly have unspecified other impact by sending crafted data to the daemon.
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Analysis
by VulDB Data Team • 01/06/2023
The vulnerability identified as CVE-2017-16548 resides within the rsync daemon implementation and specifically targets the receive_xattr function in the xattrs.c source file. This flaw affects rsync versions 3.1.2 and 3.1.3-development, representing a critical security issue that can be exploited remotely by malicious actors. The vulnerability stems from inadequate input validation mechanisms within the extended attributes processing logic, where the function fails to properly validate the termination of xattr names before proceeding with data handling operations.
The technical implementation of this vulnerability manifests through improper boundary checking in the receive_xattr function, which processes extended attributes sent to the rsync daemon. When a remote attacker sends crafted extended attribute data containing a trailing null character '' within the attribute name, the function does not validate whether this character appears in the expected position or as a legitimate terminator. This oversight creates a heap-based buffer over-read condition where the application attempts to read beyond allocated memory boundaries when processing the malformed attribute name. The buffer over-read occurs because the function assumes proper string termination and does not account for the presence of unexpected null terminators within the attribute name structure.
The operational impact of this vulnerability extends beyond simple denial of service to potentially encompass more severe consequences including application crashes and system instability. Remote attackers can leverage this weakness to cause the rsync daemon to crash repeatedly, effectively rendering the service unavailable to legitimate users and creating a persistent denial of service condition. The vulnerability's potential for unspecified other impacts suggests that under certain conditions, the heap corruption could lead to more sophisticated exploitation vectors, though the primary threat remains service disruption. This flaw represents a classic example of a buffer over-read vulnerability that can be classified under CWE-125 as an out-of-bounds read condition.
From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks. The exploitability of this weakness is particularly concerning as it requires minimal privileges and can be executed entirely through network communication with the rsync daemon. Attackers need only establish a connection to the vulnerable rsync service and send specially crafted extended attribute data to trigger the buffer over-read condition. The vulnerability does not require authentication for exploitation, making it particularly dangerous in environments where rsync daemons are exposed to untrusted networks or internet-facing services.
Mitigation strategies for CVE-2017-16548 should prioritize immediate patching of affected rsync versions to the latest stable releases that contain the necessary input validation fixes. Organizations should implement network segmentation to restrict access to rsync services and employ firewall rules to limit exposure to trusted networks only. Additionally, monitoring systems should be configured to detect unusual patterns in extended attribute processing that might indicate exploitation attempts. The vulnerability underscores the importance of proper input validation and boundary checking in security-critical applications, particularly those handling user-supplied data in network services. Organizations should also consider implementing intrusion detection systems that can identify malicious extended attribute payloads targeting this specific vulnerability pattern.