# CVE-2026-48491: Traefik: SNICheck ignores wildcard TLSOptions mappings, allowing domain-fronted mTLS bypass

> Attackers can bypass mutual TLS authentication on wildcard routers by exploiting SNICheck's failure to apply wildcard TLS options, accessing protected backends without client certificates.

- **Severity:** High 7.8 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Jun 2026
- **Updated:** 2 Sep 2026
- **Also known as:** GHSA-5r4w-85f3-pw66, GO-2026-5152, MINI-35hp-9r2c-55gh, MINI-vm74-x7qx-v6q6, MINI-vpwx-gc9h-93c9

## What is CVE-2026-48491?

CVE-2026-48491 is a high-severity authentication bypass vulnerability in Traefik Traefik, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Traefik is an HTTP reverse proxy and load balancer. From 3.7.0 until 3.7.3, there is a high severity vulnerability in Traefik's domain-fronting protection (SNICheck) that allows an unauthenticated client to bypass mutual TLS enforced through wildcard router TLSOptions. When a router uses a wildcard host rule such as Host(*.example.com) with stricter TLS options (for example RequireAndVerifyClientCert), SNICheck resolves the TLS options for the HTTP Host header using exact map lookups only and never applies wildcard matching. If another permissive SNI is served on the same entrypoint, an attacker can complete the TLS handshake under the permissive options and then send an HTTP Host header targeting the wildcard-protected backend, reaching it without presenting a client certificate. This affects the regular HTTPS / HTTP-2 path and does not require HTTP/3. This vulnerability is fixed in 3.7.3.

Weakness: CWE-807 (Reliance on Untrusted Inputs in a Security Decision), CWE-288 (Authentication Bypass Using an Alternate Path or Channel)

## Which versions are affected by CVE-2026-48491?

6 open source packages ship an affected version, including github.com/traefik/traefik/v2 and github.com/traefik/traefik/v3. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/traefik/traefik/v2` | Go | All versions | 2.11.48 |
| `github.com/traefik/traefik/v2` | Go | All versions | 2.11.48 |
| `github.com/traefik/traefik/v2` | Go | All versions | 2.11.48 |
| `github.com/traefik/traefik/v3` | Go | From 3.7.0 | 3.7.3 |
| `github.com/traefik/traefik/v3` | Go | From 3.7.0 | 3.7.3 |
| `github.com/traefik/traefik/v3` | Go | From 3.7.0 | 3.7.3 |

Products: Traefik Traefik.

## How do I fix CVE-2026-48491?

Upgrade github.com/traefik/traefik/v2 to 2.11.48 or later.

## Is CVE-2026-48491 being exploited?

There is no known exploitation of CVE-2026-48491 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-2026-48491 and fix it if it is affected.

What it is: CVE-2026-48491 is a high-severity authentication bypass vulnerability in Traefik Traefik, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-48491 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.48
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.48
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.48
- github.com/traefik/traefik/v3 (Go): affected from 3.7.0; fixed in 3.7.3
- github.com/traefik/traefik/v3 (Go): affected from 3.7.0; fixed in 3.7.3
- github.com/traefik/traefik/v3 (Go): affected from 3.7.0; fixed in 3.7.3

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-2026-48491/ (Markdown: https://insights.sbomify.com/CVE-2026-48491/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48491
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48491
- OSV: https://osv.dev/vulnerability/CVE-2026-48491

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-48491/
Summaries are generated and may contain mistakes; the official description above is the record.