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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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.
Which versions are affected by CVE-2026-1526?
4 open source packages ship an affected version, including undici. It affects 1 product.
| Package | 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 include 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
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 undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake
- CVE-2026-109869 undici vulnerable to Denial of Service via unhandled error on excessive content-encodings
- CVE-2026-87018 undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation
- CVE-2026-19534 undici vulnerable to Denial of Service via unrequested WebSocket subprotocol
- CVE-2026-12151 undici WebSocket client vulnerable to denial of service via fragment count bypass
Sources
Also known as BELL-CVE-2026-1526, CLEANSTART-2026-UZ69409, CLEANSTART-2026-WP10370, CLSA-2026-1791895514, DEBIAN-CVE-2026-1526, ECHO-3b86-4880-75c7 and 14 more.