# CVE-2026-33433: Traefik Vulnerable to BasicAuth/DigestAuth Identity Spoofing via Non-Canonical headerField > An authenticated attacker can impersonate any identity to the backend by exploiting non-canonical header field configurations in Traefik. - **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** An administrator - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 27 Mar 2026 - **Updated:** 15 Jul 2026 - **Also known as:** CLEANSTART-2026-SB40990, ECHO-f91f-26ea-bbf3, GHSA-qr99-7898-vr7c, GO-2026-4893, MINI-8xqp-fgcv-vmrf, MINI-hf3c-p65f-r4ch, MINI-q76c-8hh9-6362 ## What is CVE-2026-33433? CVE-2026-33433 is a medium-severity authentication bypass vulnerability in Traefik Traefik, published on 27 Mar 2026. An attacker needs administrator access to exploit it, with no action from the victim. ### Official description Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue. Weakness: CWE-290 (Authentication Bypass by Spoofing) ## Which versions are affected by CVE-2026-33433? 9 open source packages ship an affected version, including github.com/traefik/traefik/v3, github.com/traefik/traefik and github.com/traefik/traefik/v2. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `github.com/traefik/traefik/v3` | Go | From 3.0.0-beta1 | 3.6.12, 3.7.0-ea.3 | | `github.com/traefik/traefik/v3` | Go | From 3.0.0-beta1 | 3.6.12 | | `github.com/traefik/traefik/v3` | Go | From 3.0.0-beta1 | 3.6.12 | | `github.com/traefik/traefik/v3` | Go | From 3.7.0-ea.1 | 3.7.0-ea.3 | | `github.com/traefik/traefik/v3` | Go | From 3.7.0-ea.1 | 3.7.0-ea.3 | | `github.com/traefik/traefik` | Go | All versions | None | | `github.com/traefik/traefik/v2` | Go | All versions | 2.11.42 | | `github.com/traefik/traefik/v2` | Go | All versions | 2.11.42 | | `github.com/traefik/traefik/v2` | Go | All versions | 2.11.42 | Products: Traefik Traefik. ## How do I fix CVE-2026-33433? Upgrade github.com/traefik/traefik/v3 to a fixed version for your release line: 3.6.12 or 3.7.0-ea.3. ## Is CVE-2026-33433 being exploited? There is no known exploitation of CVE-2026-33433 in the wild and no public exploit code. ## Other vulnerabilities in Traefik Traefik - [CVE-2024-45410](https://insights.sbomify.com/CVE-2024-45410/): HTTP client can remove the X-Forwarded headers in Traefik (critical 9.8) - [CVE-2026-88877](https://insights.sbomify.com/CVE-2026-88877/): Traefik v3.7.0 Authentication Bypass via from-to-www-redirect (critical 9.3) - [CVE-2026-85595](https://insights.sbomify.com/CVE-2026-85595/): Traefik before v2.11.55 and v3.0.0 through v3.7.10 Authentication Bypass via digestAuth (critical 9.3) - [CVE-2026-88007](https://insights.sbomify.com/CVE-2026-88007/): Traefik HTTP/3 Backend NTLM Connection Reuse (critical 9.1) - [CVE-2026-88009](https://insights.sbomify.com/CVE-2026-88009/): Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing path-scoped routing, middleware guards and access logging (high 8.8) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-33433 and fix it if it is affected. What it is: CVE-2026-33433 is a medium-severity authentication bypass vulnerability in Traefik Traefik, published on 27 Mar 2026. An attacker needs administrator access to exploit it, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-33433 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/traefik/traefik/v3 (Go): affected from 3.0.0-beta1; fixed in 3.6.12, 3.7.0-ea.3 - github.com/traefik/traefik/v3 (Go): affected from 3.0.0-beta1; fixed in 3.6.12 - github.com/traefik/traefik/v3 (Go): affected from 3.0.0-beta1; fixed in 3.6.12 - github.com/traefik/traefik/v3 (Go): affected from 3.7.0-ea.1; fixed in 3.7.0-ea.3 - github.com/traefik/traefik/v3 (Go): affected from 3.7.0-ea.1; fixed in 3.7.0-ea.3 - github.com/traefik/traefik (Go): affected all versions; no fix listed - github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.42 - github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.42 - github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.42 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-33433/ (Markdown: https://insights.sbomify.com/CVE-2026-33433/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33433 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33433 - OSV: https://osv.dev/vulnerability/CVE-2026-33433 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-33433/ Summaries are generated and may contain mistakes; the official description above is the record.