Is CVE-2026-84933 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-84933 being exploited in the wild.

How severe is CVE-2026-84933?

Medium severity, with a CVSS score of 6.5, published 4 September 2026.

Which products and versions are affected?

undici (npm) SEMVER:introduced=7.0.0,fixed=7.29.1.

Is there a fix for CVE-2026-84933?

Yes. undici (npm): upgrade to 7.29.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-84933 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-84933?

Check whether you run undici (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-84933: undici cache interceptor Set-Cookie disclosure in shared caches

CVE-2026-84933 · Severity: medium · CVSS 6.5 · Published 2026-09-04

undici is a popular HTTP client library for Node.js that includes a caching interceptor to improve performance. When configured in shared-cache mode (the default), the caching layer fails to handle or strip Set-Cookie headers, causing authentication cookies from one user to be cached and re-served to other users. This allows attackers to steal session cookies and inject malicious cookies into responses seen by all subsequent users.

Technologies: undici (npm). Vendors: npm.

Quick answers

Is CVE-2026-84933 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-84933 being exploited in the wild.
How severe is CVE-2026-84933?: Medium severity, with a CVSS score of 6.5, published 4 September 2026.
Which products and versions are affected?: undici (npm) SEMVER:introduced=7.0.0,fixed=7.29.1.
Is there a fix for CVE-2026-84933?: Yes. undici (npm): upgrade to 7.29.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-84933 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-84933?: Check whether you run undici (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

undici (npm): upgrade to 7.29.1 or later
```
npm install undici@7.29.1
```

Technical details

The vulnerability is a sensitive information exposure (CWE-200) and improper cache handling (CWE-524) in undici's cache interceptor. The root cause is that the cache path does not validate or strip Set-Cookie response headers before storing cacheable responses marked with public cache directives. When multiple clients hit the same cache key, a cached Set-Cookie from one client is re-served to others, violating RFC 6265 section 7.2 which requires shared caches to never store cookies. The attack requires network access to undici in shared-cache mode (default configuration) and targets multi-user or untrusted upstream scenarios. Patches are available in versions 7.29.1 and 8.10.2, which prevent storage and re-serving of responses containing Set-Cookie headers in shared-cache mode.

Affected products

OpenJS Foundation undici 7.0.0 to 7.29.0, 8.0.0 to 8.10.1

Identifiers

CVE-2026-84933
GHSA-2jfj-6hjv-fm6j

Timeline

2026-09-04: disclosed
2026-09-04: patched: Patches released in undici 7.29.1 and 8.10.2

References

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