# CVE-2026-66749: Let's Chat 0.4.0 - 0.4.8 Denial of Service via Null Dereference in Room Lookup

> Authenticated attackers can crash the Let's Chat server by sending a crafted request with a non-existent room ID, causing a null dereference.

- **Severity:** High 7.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 28 Jul 2026
- **Updated:** 28 Jul 2026
- **Also known as:** GHSA-qjpw-62vp-8j4q

## What is CVE-2026-66749?

CVE-2026-66749 is a high-severity vulnerability in sdelements lets-chat, published on 28 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Let's Chat 0.4.0 through 0.4.8 contains a null dereference vulnerability that allows authenticated attackers to crash the server by supplying a valid 24-character hex string room parameter that matches no document in the database. Attackers can send a crafted GET /messages request causing an uncaught TypeError in an asynchronous Mongoose callback that terminates the Node.js server process, with the same defect reachable through multiple code paths including the socket.io interface.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-66749?


## How do I fix CVE-2026-66749?

No fix has been published for CVE-2026-66749 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-66749 being exploited?

There is no known exploitation of CVE-2026-66749 in the wild and no public exploit code.

Public exploit code:

- Security Advisory: Unchecked Room Lookup Leads to Server Crash (Let's Chat) (github_poc): https://github.com/theopaid/CVE-2026-66749-Unchecked-Room-Lookup-Leads-to-Server-Crash-Let-s-Chat-

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66749 and fix it if it is affected.

What it is: CVE-2026-66749 is a high-severity vulnerability in sdelements lets-chat, published on 28 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-66749 in the wild and no public exploit code.

Affected product: sdelements lets-chat. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-66749/ (Markdown: https://insights.sbomify.com/CVE-2026-66749/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66749
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66749
- OSV: https://osv.dev/vulnerability/CVE-2026-66749

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66749/
Summaries are generated and may contain mistakes; the official description above is the record.