CVE-2025-46332: Information Disclosure via Flags override link
Summary
An information disclosure vulnerability affecting Flags SDK has been addressed. It impacted flags ≤3.2.0 and @vercel/flags ≤3.1.1 and in certain circumstances, allowed a bad actor with detailed knowledge of the vulnerability to list all flags returned by the flags discovery endpoint (.well-known/vercel/flags).
Impact
This vulnerability allowed for information disclosure, where a bad actor could gain access to a list of all feature flags exposed through the flags discovery endpoint, including the:
- Flag names - Flag descriptions - Available options and their labels (e.g. true, false) - Default flag values
Not impacted:
- Flags providers were not accessible
No write access nor additional customer data was exposed, this is limited to just the values noted above. Vercel has automatically mitigated this incident on behalf of our customers for the default flags discovery endpoint at .well-known/vercel/flags. Flags Explorer will be disabled and show a warning notice until upgraded to flags@4.0.0.
Resolution
The verifyAccess function was patched within flags@4.0.0.
Users of @vercel/flags should also migrate to flags@4.0.0.
For further guidance on upgrading your version, please see our upgrade guide.
Mitigations
Vercel implemented a network-level mitigation to prevent the default flags discovery endpoint at /.well-known/vercel/flags being reachable, which automatically protects Vercel deployments against exploitation of this issue. Users need to upgrade to flags@4.0.0 to re-enable the Flags Explorer.
This automatic mitigation is not effective in two scenarios:
- When using the Flags SDK on Pages Router, as the original non-rewritten route would still be accessible, e.g. /api/vercel/flags. - When using a custom path for the flags discovery endpoint.
If you are not protected by the Vercel default mitigation you can temporarily deny access to the other exposed flags discovery endpoints through a custom WAF rule while you upgrade to the latest version.
References
- https://vercel.com/changelog/information-disclosure-in-flags-sdk-cve-2025-46332 - https://github.com/vercel/flags/blob/main/packages/flags/guides/upgrade-to-v4.md
Other sources
Flags SDK is an open-source feature flags toolkit for Next.js and SvelteKit. Impacted versions include flags from 3.2.0 and prior and @vercel/flags from 3.1.1 and prior as certain circumstances allows a bad actor with detailed knowledge of the vulnerability to list all flags returned by the flags discovery endpoint (.well-known/vercel/flags). This vulnerability allows for information disclosure, where a bad actor could gain access to a list of all feature flags exposed through the flags discovery endpoint, including the flag names, flag descriptions, available options and their labels (e.g. true, false), and default flag values. This issue has been patched in flags@4.0.0, users of flags and @vercel/flags should also migrate to flags@4.0.0.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2025-46332?
CVE-2025-46332 is considered a high severity vulnerability due to its potential for information disclosure.
How do I fix CVE-2025-46332?
To fix CVE-2025-46332, upgrade to Flags SDK version 3.2.1 or later and @vercel/flags version 3.1.2 or later.
What types of applications are affected by CVE-2025-46332?
CVE-2025-46332 affects applications using Flags SDK versions 3.2.0 and below and @vercel/flags versions 3.1.1 and below.
What impact does CVE-2025-46332 have on application security?
CVE-2025-46332 allows unauthorized access to sensitive feature flags, potentially leading to unauthorized features being activated.
Is there a workaround for CVE-2025-46332 if I cannot immediately upgrade?
There is no known workaround for CVE-2025-46332; upgrading to patched versions is required to mitigate the risk.