External risk intelligence

Rsync Daemon Heap-Based Buffer Overflow Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2024-12084

The vulnerability affects the rsync daemon. While rsync is a common utility for file synchronization, it is typically used for internal data movement, backup processes, or restricted site-to-site transfers. While it can be exposed to the internet, it is not a standard internet-facing web application or edge gateway service in most common deployments.

Out-of-bounds Write

Samba Rsync

3.2.73.3.010.0before 24.1124.11before 20250123

Halo Surface Signal: 3 out of 5 — possibly public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical security vulnerability has been identified in the rsync daemon, a tool used for file synchronization. This flaw, a buffer overflow, could allow unauthorized individuals to gain control over affected systems if exploited. The main concern at this time is to confirm if this specific technology is in use within our environment and to what extent.

Flaw allows unauthorized code execution in file sync software.
Critical issue impacts network-accessible data transfer tools.
Confirm rsync usage; assess potential exposure.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending specially crafted data to an exposed rsync daemon. The daemon processes this data without properly validating the length of checksums, leading to an out-of-bounds write on the heap. This could allow an attacker to overwrite critical memory, potentially leading to code execution or denial of service.

Network access to the rsync daemon is required.
A crafted checksum length triggers the overflow.
Risk includes code execution or denial of service.

Live Threat

Current exploitation, exposure, and threat context

A heap-based buffer overflow in the rsync daemon could allow an attacker to write out of bounds when handling specific checksum lengths. This may lead to a crash or potential corruption of memory used by the rsync process.

rsync daemon memory
Improper handling of checksum lengths
Service instability or corruption

Operational Fix

Recommended remediation, mitigation, and detection steps

Teams responsible for rsync daemons, likely infrastructure or platform teams, should initiate by locating all instances and assessing their exposure and criticality. Once identified, the accountable owner must be confirmed before planning remediation or mitigation strategies.

Own the issue: Infrastructure or platform teams.
Verify first: Instance exposure and business criticality.
Action follows: Plan remediation based on risk.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is rsync and how is it used?

rsync is a widely used software utility for synchronizing files and directories between locations. It is commonly employed by administrators for system backups, mirroring data across servers, and managing file transfers. The rsync daemon specifically allows the program to run as a background service, enabling remote systems to connect and exchange data efficiently over a network.

How does CVE-2024-12084 affect memory?

This vulnerability is a heap-based buffer overflow, classified under CWE-122 and CWE-787. It occurs because the rsync daemon fails to correctly check the length of data provided by a user during synchronization. When the checksum length exceeds the fixed capacity of the allocated memory buffer, it writes data beyond its intended boundaries. This memory corruption can cause the service to crash or potentially allow for unauthorized code execution.

What triggers this buffer overflow?

An attacker triggers the vulnerability by sending a specially crafted checksum length to an active rsync daemon. The daemon attempts to process this unexpected input, which results in the out-of-bounds write. It is important to note that this flaw specifically relates to the handling of checksum data; standard, legitimate file synchronization tasks that do not involve malformed checksum length values will not trigger this memory error.

Is my rsync daemon at risk of exploitation?

According to Halo Surface Signal, this vulnerability is classified as external because it can be exploited over a network. However, while rsync is often used for internal data movement or site-to-site backups, its risk depends on whether your daemon is reachable from untrusted networks. If your instance is not exposed to the internet, the likelihood of an external actor successfully initiating the attack path is significantly lower than if it were an internet-facing service.

What steps should I take if I run rsync?

Begin by identifying all running instances of the rsync daemon within your infrastructure. Once located, verify their network configuration to determine if they are accessible from external sources versus restricted internal zones. After establishing the inventory and exposure level, consult your distribution or vendor update channels to plan for the appropriate software patches or security configurations that address this heap-based overflow.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.