# Vault timing side-channel username enumeration

Source: https://startwithidentity.com/cves/cve-2025-6011/
Last updated: 2026-08-29
License: content by Start with Identity. Cite the source URL.

---

## What broke

Vault took a measurably different amount of time to reject an unknown username versus a known one. That is a timing side-channel for username enumeration, next to the explicit error leak in [CVE-2025-6010](https://startwithidentity.com/cves/cve-2025-6010/). Fixed in 1.20.2.

## Why it matters

Closing the error string and leaving the timing is how enumeration advisories come back a quarter later. Take both IDs in the same change.

## What to do

- Upgrade. If you still expose Userpass, pad auth responses to a constant time on your reverse proxy as defense in depth.
- Prefer SSO. Enumeration only matters if the attacker can hit the login method.

## After you patch

A vault compromise is not one credential, it is every credential the vault held or could issue.

- **Rotate everything in scope**, including secrets the vault issued dynamically during the exposure window, because a lease that was valid then may still be valid now.
- **Revoke active leases and tokens**, then review the audit device log for reads you cannot attribute to a known workload.
- **Rotate the vault's own credentials**: unseal or recovery keys, root tokens, and any authentication backend configuration that could be used to re-enter.
- **Rotate downstream credentials the vault brokered**, cloud roles, database users, and PKI certificates, since the point of the vault is that it can mint them. See [secrets rotation](https://startwithidentity.com/glossary/secrets-rotation/) and [what is secrets management](https://startwithidentity.com/guides/fundamentals/what-is-secrets-management/).

## Sources

- [NVD: CVE-2025-6011](https://nvd.nist.gov/vuln/detail/CVE-2025-6011)