# CVE-2021-32813: Drop Headers via Malicious Connection Header

> Traefik reverse proxy allows attackers to strip security headers via malicious Connection headers, potentially bypassing middleware protections.

- **Severity:** Medium 4.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Aug 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ECHO-ef09-14ab-a33b, GHSA-m697-4v8f-55qg, GO-2022-0923

## What is CVE-2021-32813?

CVE-2021-32813 is a medium-severity vulnerability in Traefik Traefik, published on 3 Aug 2021. 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. Prior to version 2.4.13, there exists a potential header vulnerability in Traefik's handling of the Connection header. Active exploitation of this issue is unlikely, as it requires that a removed header would lead to a privilege escalation, however, the Traefik team has addressed this issue to prevent any potential abuse. If one has a chain of Traefik middlewares, and one of them sets a request header, then sending a request with a certain Connection header will cause it to be removed before the request is sent. In this case, the backend does not see the request header. A patch is available in version 2.4.13. There are no known workarounds aside from upgrading.

Weakness: CWE-913 (Improper Control of Dynamically-Managed Code Resources)

## Which versions are affected by CVE-2021-32813?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/traefik/traefik` | Go | All versions | None |
| `github.com/traefik/traefik` | Go | All versions to 1.7.30 | None |
| `github.com/traefik/traefik` | Go | All versions to 1.7.30 | None |
| `github.com/traefik/traefik/v2` | Go | All versions | 2.4.13 |
| `github.com/traefik/traefik/v2` | Go | All versions | 2.4.13 |
| `github.com/traefik/traefik/v2` | Go | All versions | 2.4.13 |

Products: Traefik Traefik.

## How do I fix CVE-2021-32813?

Upgrade to a fixed version.

## Is CVE-2021-32813 being exploited?

There is no known exploitation of CVE-2021-32813 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-2021-32813 and fix it if it is affected.

What it is: CVE-2021-32813 is a medium-severity vulnerability in Traefik Traefik, published on 3 Aug 2021. 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-2021-32813 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/traefik/traefik (Go): affected all versions; no fix listed
- github.com/traefik/traefik (Go): affected all versions up to 1.7.30; no fix listed
- github.com/traefik/traefik (Go): affected all versions up to 1.7.30; no fix listed
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.4.13
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.4.13
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.4.13

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-2021-32813/ (Markdown: https://insights.sbomify.com/CVE-2021-32813/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32813
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32813
- OSV: https://osv.dev/vulnerability/CVE-2021-32813

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32813/
Summaries are generated and may contain mistakes; the official description above is the record.