⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Medium · CVSS 6.9

How to Fix CVE-2026-43620: Out-of-Bounds Read in rsync

Other vulnerabilities in the same area that are worth patching alongside this one:

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 6.9 - Medium
Actively exploited?Not currently listed in CISA KEV
Affected0 < 3.4.3
Fixed inSee vendor advisory
Type (CWE)CWE-125: Out-of-bounds Read

What is CVE-2026-43620?

CVE-2026-43620 is an out-of-bounds read in rsync. A malformed input causes the product to read memory past the intended buffer boundary, which leaks adjacent process memory and in some cases crashes the service. Vendor description: Rsync version 3.4.2 and prior contain a receiver-side out-of-bounds array read vulnerability in recv_files() in receiver.c that allows a malicious rsync server to crash the rsync client process. Attackers can exploit the vulnerability by setting CF_INC_RECURSE in compatibility flags and sending a specially crafted file list where the first sorted entry is not the leading dot directory, followed by a transfer record with ndx=0 and an iflag word without ITEM_TRANSFER, causing the receiver to read 8 bytes before the allocated pointer array and dereference an invalid pointer at an unmapped address, resulting in a deterministic SIGSEGV crash of the rsync client.

Why this CVE matters

Out-of-bounds read flaws in a network-facing service produce information disclosure today and are routinely the first half of a two-bug chain that ends in code execution.

For deployments of rsync that have been exposed to the public internet during the disclosure window, the operating assumption should be that scanning has already happened. Even where exploitation has not been publicly observed, scanning for the vulnerable fingerprint is cheap and routine. Patching closes the door; log review and credential rotation close out the rest of the response.

Am I affected?

You are affected if your installation matches any of these version ranges:

Check your installed version against the list above. If you cannot determine the version, treat the system as affected and follow the upgrade path below.

Open rsync's About dialog or run the vendor-documented version-check command. Compare the result against the affected ranges in the advisory.

How to fix CVE-2026-43620

  1. Read the vendor advisory in full: https://github.com/RsyncProject/rsync/security/advisories/GHSA-28pw-r563-rxvm
  2. Upgrade rsync to the patched build listed in the vendor advisory.
  3. Back up the configuration (and database, where applicable) before upgrading.
  4. Apply the patch in a maintenance window. For HA pairs, upgrade the standby node first, fail over, then upgrade the former primary.
  5. Restart the affected service so the patched binary loads, then verify the new version (see verification section).

Upgrade RsyncProject rsync


# CVE-2026-43620 affects rsync 0 < 3.4.3.
# Fixed in 3.4.3. Vendor advisory: https://github.com/RsyncProject/rsync/security/advisories/GHSA-28pw-r563-rxvm

# 1. Identify the running version using the vendor-documented command.
#    (Open the product UI -> About, or run the CLI version probe.)

# 2. Stage the patched build named in the advisory.
#    Vendor advisory: https://github.com/RsyncProject/rsync/security/advisories/GHSA-28pw-r563-rxvm

# 3. Apply the upgrade. If the vendor ships a Linux package, pull it via your
#    distribution's package manager:
sudo apt update && sudo apt install --only-upgrade rsync        # Debian / Ubuntu
sudo dnf upgrade rsync                                          # RHEL / Rocky / Alma / Fedora

# 4. Restart the affected service so the new binary loads.
sudo systemctl restart rsync 2>/dev/null || true

# 5. Re-run the version probe and confirm it matches 3.4.3.


# Windows-hosted installs of rsync: apply via PSWindowsUpdate or the vendor MSI.
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck -Confirm:$false
Get-WindowsUpdate -AcceptAll -Install -AutoReboot

Verify the fix landed


# CVE-2026-43620 verification checklist.

# 1. Confirm the running version matches 3.4.3 (replace the version probe with
#    the platform-specific command shown above).

# 2. Re-scan the host with your vulnerability scanner (Nessus, Qualys, Tenable,
#    OpenVAS, Wazuh). The scanner must no longer flag CVE-2026-43620.

# 3. Inspect recent service and kernel logs for crash-loops or rollback events.
journalctl -u <service-name> --since "10 minutes ago"
dmesg --since "10 minutes ago"

# 4. Cross-check the running build against the vendor advisory:
#    https://github.com/RsyncProject/rsync/security/advisories/GHSA-28pw-r563-rxvm

If you cannot patch immediately

Block network reachability to the affected service from untrusted networks. The patched build is the only durable fix; memory-disclosure bugs cannot be fully neutralized at the network layer.

How to verify the fix worked

If your installation was internet-reachable during the disclosure window, treat log review as part of the remediation rather than an optional follow-up. Look for log entries that do not match your normal request patterns, especially repeated requests to the same uncommon endpoint, and any administrative changes you cannot tie back to a known operator.

Frequently asked questions

Is CVE-2026-43620 being exploited in the wild?

Public exploitation has not been confirmed by CISA at the time of writing. Treat the patch as time-sensitive anyway; reports often lag actual abuse.

Will a WAF or IDS rule fully mitigate CVE-2026-43620?

No. Network-layer filters can reduce noise and slow opportunistic scanners, but they will not stop a determined attacker. The vendor patch is the only durable fix.

How long should I plan for the upgrade?

Typical vendor-documented upgrade windows for rsync run from a few minutes to under an hour depending on cluster size. Test in a staging environment first and follow the vendor's documented HA upgrade order.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*