CVE-2023-40515: High Input Validation DoS in LG Simple Editor

CVE-2023-40515 is a high flaw in LG Simple Editor 3.21.0: the joinAddUser method has an improper input validation that causes denial of service. NVD scores it 7.5 (High). LG told the Zero Day Initiative it will not fix it, so no patch exists. Restrict access to the application or remove it.

What's affected

The record lists one product and one version: LG Simple Editor 3.21.0 (the CPE vendor field reads lg). The weakness class is CWE-20.

The vulnerable code is the joinAddUser method, which does not validate input properly, which the advisory says lets an unauthenticated remote attacker create a denial of service condition. The record scores availability as high with no confidentiality or integrity impact, so the harm is an outage rather than data loss.

No fixed version exists. The Zero Day Initiative advisory ZDI-23-1197 (tracked as ZDI-CAN-20048) says ZDI reported the issue to LG on 14 February 2023. On 8 August 2023 the vendor stated it does not plan to fix it now or in the future. ZDI then published it as a zero day advisory on 24 August 2023. NVD added the record on 3 May 2024. The record does not say whether versions other than 3.21.0 are affected, and the advisory names no safe version.

It is not in CISA's Known Exploited Vulnerabilities catalog, and the advisory does not say it is exploited in the wild.

How to check if you're exposed

There is no package feed to scan for this one, so exposure comes down to whether the application is installed and reachable. The record lists no authentication requirement, so network reachability is the only barrier.

On a Windows host, check whether LG Simple Editor is installed and which version:

Get-Package | Where-Object Name -like "*Simple Editor*"

Also look in Apps and features, because not every installer registers with that command. Then list listening sockets and match the owning process to the application:

netstat -ano | findstr LISTENING
tasklist /FI "PID eq 1234"

Replace 1234 with a process ID from the first command. If you find version 3.21.0 and the service answers from any network other than a trusted administration segment, treat the host as exposed. Add the host to your software inventory either way, so a later fix notice from LG reaches someone who can act on it.

What to do now

1. Inventory every host that has LG Simple Editor installed and record the version.
2. Remove network access you do not need. Block inbound connections to the service at the host firewall and the perimeter, and allow only named administrators.
3. If the product is not in active use, uninstall it. With no vendor fix, retirement is the only complete remedy.
4. Watch for service crashes or restarts and for requests to this method from unexpected sources.
5. Ask LG whether a patched version or a replacement exists, and recheck the Zero Day Initiative advisory for updates.

Why it matters

Improper input validation is the broadest weakness class in the catalog, CWE-20. Programs that accept values without checking type, size or format can crash, hang or loop on a malformed one. A single request from an unauthenticated caller is enough when the service is reachable.

The advisory gives no detail on the failure mode beyond the denial of service, so this post makes no claims about how it behaves. Practical planning is simple: assume a stranger who can reach the service can take it down. The vendor has said it will not patch this, which is the main reason the guidance here is about reducing exposure.

This is one of many records filed against LG Simple Editor 3.21.0 from the same ZDI batch, each tied to a different method. Each bug stands alone, so the safest reading is that the product as a whole should stay off untrusted networks.

Quick check

Sources

• Zero Day Initiative advisory ZDI-23-1197
• Safeguard Gold entry for CVE-2023-40515
• NVD record for CVE-2023-40515, as supplied in the Safeguard CVE dataset

Last reviewed: 19 October 2026.