Rsync CVE-2026-43618: Integer Overflow Exposes Memory, Bypasses ASLR
The National Vulnerability Database (NVD) has disclosed CVE-2026-43618, a high-severity integer overflow vulnerability impacting Rsync versions 3.4.2 and prior. This flaw resides in the compressed-token decoder, where a 32-bit signed counter lacks proper overflow checks. A malicious sender can exploit this to trigger an overflow, forcing the receiver process to read and return data beyond intended buffer boundaries.
This isn’t just a crash; it’s a critical information disclosure. According to the NVD, successful exploitation can leak sensitive process memory contents. This includes environment variables, passwords, heap and stack data, and even library memory pointers. For attackers, this significantly degrades Address Space Layout Randomization (ASLR) effectiveness, simplifying subsequent exploitation efforts and making deeper system compromise far more feasible.
Defenders relying on Rsync for data synchronization need to take this seriously. While the NVD has not specified particular affected products, any environment utilizing vulnerable Rsync versions is at risk. This is a pre-authentication memory leak that attackers can leverage to map out your systems and prepare for a more targeted strike.
What This Means For You
- If your organization uses Rsync, specifically versions 3.4.2 or older, you are exposed. This isn't theoretical; an attacker can exfiltrate sensitive memory contents, including credentials and ASLR bypass data, without prior authentication. Prioritize patching or upgrading your Rsync instances immediately. Do not wait for active exploitation.
Related ATT&CK Techniques
🛡️ Detection Rules
3 rules · 6 SIEM formats3 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
Rsync Integer Overflow - Rsync Daemon Network Connection - CVE-2026-43618
title: Rsync Integer Overflow - Rsync Daemon Network Connection - CVE-2026-43618
id: scw-2026-05-20-ai-1
status: experimental
level: high
description: |
Detects the execution of the rsync daemon in server mode, which is a prerequisite for exploiting CVE-2026-43618. This vulnerability allows an attacker to trigger an integer overflow in the compressed-token decoder, leading to memory disclosure and bypass of ASLR. This rule specifically targets the rsync server process, which is the target of the exploit.
author: SCW Feed Engine (AI-generated)
date: 2026-05-20
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-43618/
tags:
- attack.initial_access
- attack.t1190
logsource:
category: process_creation
detection:
selection:
Image|endswith:
- 'rsync.exe'
CommandLine|contains:
- '--server'
condition: selection
falsepositives:
- Legitimate administrative activity
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-43618 | Information Disclosure | Rsync version 3.4.2 and prior |
| CVE-2026-43618 | Buffer Overflow | Integer overflow in compressed-token decoder |
| CVE-2026-43618 | Memory Corruption | 32-bit signed counter overflow leading to out-of-bounds read |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 20, 2026 at 05:16 UTC |
This content was AI-rewritten and enriched by Shimi's Cyber World based on the original source. All intellectual property rights remain with the original author.
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