CVE-2026-42239: Budibase insecure session cookie configuration leads to account takeover

CVE-2026-42239 · Severity: high · CVSS 8.1 · Published 2026-05-07

Budibase is a low-code platform for building business applications and automations. The authentication session cookie is configured without the httpOnly flag, allowing any JavaScript code running on the page—including code injected via XSS vulnerabilities—to read and steal the session token. An attacker can weaponize this by combining it with known XSS flaws to gain persistent access to victim accounts.

Technologies: Budibase Backend-Core, @budibase/backend-core (npm). Vendors: Budibase, npm.

Quick answers

Is CVE-2026-42239 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42239 being exploited in the wild.
How severe is CVE-2026-42239?
High severity, with a CVSS score of 8.1, published 7 May 2026.
Which products and versions are affected?
Budibase Backend-Core < 3.35.10, <3.35.10; @budibase/backend-core (npm) < 3.35.10, SEMVER:introduced=0,fixed=3.35.10.
Is there a fix for CVE-2026-42239?
Yes. @budibase/backend-core (npm): upgrade to 3.35.10 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42239 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-42239?
Check whether you run Budibase Backend-Core or @budibase/backend-core (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

  • @budibase/backend-core (npm): upgrade to 3.35.10 or later
    npm install @budibase/backend-core@3.35.10

Technical details

The vulnerability exists in packages/backend-core/src/utils/utils.ts where the budibase:auth cookie—containing a signed JWT session token—is set with httpOnly: false. This allows any JavaScript execution context (XSS payload, malicious browser extension, injected script) to read the full session token via document.cookie and exfiltrate it to an attacker-controlled server. The cookie additionally lacks the secure flag (should prevent HTTP transmission) and sameSite attribute (should mitigate cross-site request attacks). When chained with stored XSS vulnerabilities in entity names (GHSA-gp5x-2v54-v2q5), an attacker can create a malicious entity that steals the JWT of any user who views it, granting persistent account access. The configuration is hardcoded across all Budibase deployments. The fix is to set httpOnly: true, secure: true, and sameSite: 'lax' in the cookie configuration. Patch available in version 3.35.10.

Affected products

  • Budibase @budibase/backend-core <3.35.10

Identifiers

  • CVE-2026-42239
  • GHSA-4f9j-vr4p-642r

Timeline

  • 2026-04-24: disclosed: GHSA-4f9j-vr4p-642r published
  • 2026-04-21: patched: Fixed in version 3.35.10

References

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