# CVE-2026-88010: Traefik BasicAuth singleflight username enumeration via timing oracle

Source: https://junglewise.ai/threats/cve-2026-88010-traefik-basicauth-singleflight-username-enumeration-via-timing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-22. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-88010 · Severity: medium · CVSS 4 · Published 2026-09-22

Traefik's BasicAuth middleware can leak whether a username exists on the system through timing differences when multiple login requests are sent concurrently. An attacker can send overlapping credential attempts and measure response times to determine if a given username is valid—faster responses indicate a non-existent user, while slower responses indicate the user exists. This allows attackers to enumerate valid usernames without needing correct passwords, potentially aiding account-targeting attacks.

Technologies: [github.com/traefik/traefik (Go)](https://junglewise.ai/threats/technologies/github-com-traefik-traefik), [Traefik](https://junglewise.ai/threats/technologies/traefik). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Traefik](https://junglewise.ai/threats/vendors/traefik).

## Quick answers

**Is CVE-2026-88010 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-88010 being exploited in the wild.

**How severe is CVE-2026-88010?** Medium severity, with a CVSS score of 4, published 22 September 2026.

**Which products and versions are affected?** github.com/traefik/traefik (Go) SEMVER:introduced=0; Traefik (Go) SEMVER:introduced=3.6.11,fixed=3.7.13; Traefik v3.6.11 through v3.7.12.

**Is there a fix for CVE-2026-88010?** Yes. Traefik (Go): upgrade to 3.7.13 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-88010 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-88010?** Check whether you run github.com/traefik/traefik (Go), Traefik (Go) or Traefik 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

- Traefik (Go): upgrade to 3.7.13 or later

  ```sh
  go get Traefik@v3.7.13
  ```


## Technical details

The vulnerability is a timing oracle in Traefik's BasicAuth middleware that exploits request-coalescing logic intended to deduplicate password hashes. The singleflight deduplication key was constructed from the submitted password plus the stored secret, causing all non-existent usernames to share a single key while each real username had its own key. Under concurrent load, a probe request can race an attacker-controlled leader request: if the username does not exist, the probe receives the leader's fast cached result (coalesced); if the username exists, the probe computes its own hash (slow). This reintroduces a username-enumeration side-channel despite the presence of a `notFoundSecret` dummy hash intended to equalize sequential lookup costs. The attack requires attacker-controlled concurrency and network access but no authentication. The fix changes the singleflight key derivation to use only submitted credentials (username + password), removing the existence-dependent partitioning. Affected versions: Traefik v3.6.11 through v3.7; v2 and Digest Auth are unaffected.

## Affected products

- Traefik Traefik v3.6.11 through v3.7.12

## Identifiers

- CVE-2026-88010
- GHSA-8fcf-v89g-xpg6
- GO-2026-6558

## Timeline

- 2026-09-22: disclosed
- 2026-09-22: patched: Fixed in v3.7.13
- 2026-09-22: advisory: GHSA-8fcf-v89g-xpg6

## Related threats

- [Traefik ForwardAuth connection pool identity leak via NTLM/Negotiate](https://junglewise.ai/threats/cve-2026-121966-traefik-2-x-before-2-11-60-and-3-x-before-3-7-16-sends)
- [Traefik FastProxy data race in HTTP/1 upgrades](https://junglewise.ai/threats/cve-2026-119574-traefik-from-3-2-0-before-3-7-15-contains-a-data-race-in-the)
- [Traefik authentication bypass in TLS options resolution](https://junglewise.ai/threats/cve-2026-114656-traefik-before-2-11-58-and-3-7-13-contains-an-authentication)
- [Traefik NTLM/Kerberos TLS configuration bypass](https://junglewise.ai/threats/cve-2026-114642-traefik-2-11-0-before-2-11-58-and-3-0-0-before-3-7-14-stores-its)
- [Traefik authentication bypass in backend connection pool](https://junglewise.ai/threats/cve-2026-114639-traefik-2-11-0-before-2-11-58-and-3-0-0-before-3-7-14-contains)