CVE-2026-43620
Description
A flaw was found in rsync. A malicious rsync server can exploit an out-of-bounds read vulnerability in the recv_files() function. By manipulating compatibility flags and transfer records, the server can cause a connecting client to attempt to read memory outside of allocated bounds. This can lead to a segmentation fault, resulting in a denial of service for the client.
Statement
This Moderate impact flaw in rsync clients allows a remote, unauthenticated attacker to cause a denial-of-service by crafting a malicious rsync server. When a client pulls from such a server, an out-of-bounds read occurs due to an incomplete fix, leading to a deterministic crash. This affects any rsync client performing a normal pull from an attacker-controlled URL, as the inc_recurse option, which is enabled by default, facilitates the exploit.
Mitigation
To mitigate this issue, rsync clients can be configured to disable incremental recursion when pulling from untrusted sources. This can be achieved by using the `--no-inc-recursive` option.
Example:
`rsync --no-inc-recursive [OPTIONS] SOURCE DESTINATION`
Disabling incremental recursion may affect the efficiency of transfers for large, frequently updated directories.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.5 | 5.5 | 6.5 |
| Attack Vector | Network | Local | Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | Low | None | None |
| User Interaction | None | Required | Required |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | None | None | None |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
Confidentiality
Technical Impact: Bypass Protection Mechanism
Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
Other
Technical Impact: Varies by Context
The read operation could produce other undefined or unexpected results.
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