# CVE-2026-1526: undici is vulnerable to Unbounded Memory Consumption in undici WebSocket permessage-deflate Decompression

> A malicious WebSocket server can crash the Node.js process by sending a decompression bomb that exhausts memory during permessage-deflate decompression.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Mar 2026
- **Updated:** 14 Sep 2026
- **Also known as:** BELL-CVE-2026-1526, CLEANSTART-2026-UZ69409, CLEANSTART-2026-WP10370, CLSA-2026-1791895514, DEBIAN-CVE-2026-1526, ECHO-3b86-4880-75c7, GHSA-vrm6-8vpv-qv8q, MINI-2mhj-2953-qwm3, MINI-4xr9-w754-f98g, MINI-583m-pf4j-63v2, MINI-645f-xjfq-8h33, MINI-8gpf-7426-fwxr, MINI-9gjx-q8pg-62gp, MINI-hh4j-qc5p-6q23, MINI-hhcp-66qp-wg3q, MINI-hx6g-x97x-w656, MINI-j8wf-3wm4-hvqp, MINI-mmf6-mxcf-4qp2, ROOT-APP-NPM-CVE-2026-1526, UBUNTU-CVE-2026-1526

## What is CVE-2026-1526?

CVE-2026-1526 is a high-severity denial of service vulnerability in Nodejs Undici, published on 12 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive.

The vulnerability exists in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-409 (Improper Handling of Highly Compressed Data (Data Amplification))

## Which versions are affected by CVE-2026-1526?

4 open source packages ship an affected version, including undici. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `undici` | npm | All versions | 6.24.0 |
| `undici` | npm | All versions | 6.24.0 |
| `undici` | npm | From 7.0.0 | 7.24.0 |
| `undici` | npm | From 7.0.0 | 7.24.0 |

Products: Nodejs Undici.

## How do I fix CVE-2026-1526?

Upgrade undici to a fixed version for your release line: 6.24.0 or 7.24.0.

## Is CVE-2026-1526 being exploited?

There is no known exploitation of CVE-2026-1526 in the wild and no public exploit code.

## Other vulnerabilities in Nodejs Undici

- [CVE-2026-109855](https://insights.sbomify.com/CVE-2026-109855/): undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake (high 7.5)
- [CVE-2026-109869](https://insights.sbomify.com/CVE-2026-109869/): undici vulnerable to Denial of Service via unhandled error on excessive content-encodings (high 7.5)
- [CVE-2026-87018](https://insights.sbomify.com/CVE-2026-87018/): undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation (high 7.5)
- [CVE-2026-19534](https://insights.sbomify.com/CVE-2026-19534/): undici vulnerable to Denial of Service via unrequested WebSocket subprotocol (high 7.5)
- [CVE-2026-12151](https://insights.sbomify.com/CVE-2026-12151/): undici WebSocket client vulnerable to denial of service via fragment count bypass (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-1526 and fix it if it is affected.

What it is: CVE-2026-1526 is a high-severity denial of service vulnerability in Nodejs Undici, published on 12 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-1526 in the wild and no public exploit code.

Affected packages and fixed versions:
- undici (npm): affected all versions; fixed in 6.24.0
- undici (npm): affected all versions; fixed in 6.24.0
- undici (npm): affected from 7.0.0; fixed in 7.24.0
- undici (npm): affected from 7.0.0; fixed in 7.24.0

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-2026-1526/ (Markdown: https://insights.sbomify.com/CVE-2026-1526/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-1526
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-1526
- OSV: https://osv.dev/vulnerability/CVE-2026-1526

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-1526/
Summaries are generated and may contain mistakes; the official description above is the record.