CVE-2026-33433: Traefik is an HTTP reverse proxy and load balancer

This month

HIGH 8.8UPGRADE

CVE-2026-33433 is a high-severity flaw (CVSS 8.8) affecting traefik. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.5% (top 58%)
CISA exploited list	No
Weakness	CWE-290
Published	2026-03-27
Last modified	2026-07-15

Publisher (CNA): GitHub, Inc. · Vendor: traefik

Last updated 2026-07-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-27 15:16 UTCPublished CVE record published
2026-07-15 02:20 UTCUpdated Record last modified

traefik traefik UPGRADE

Affected: < 2.11.42 · >= 3.0.0 and < 3.6.12 · 3.7.0 ea1 · 3.7.0 ea2

Fixed in: 2.11.42, 3.6.12

Safe to downgrade to: a release before 3.0.0

1. Check installed version

apt-cache policy traefik || rpm -q traefik || traefik --version

2. UPGRADE to 2.11.42 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade traefik

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade traefik

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.0.0 (Debian / Ubuntu)

apt-cache madison traefik sudo apt install traefik=<VERSION_BEFORE_3.0.0> sudo apt-mark hold traefik

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list traefik sudo dnf downgrade traefik-<VERSION_BEFORE_3.0.0> sudo dnf versionlock add traefik

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-33433?

traefik: upgrade to 2.11.42, 3.6.12. Exact commands for each OS are on this page.

Is CVE-2026-33433 being exploited?

CVE-2026-33433 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-33433 affect?

CVE-2026-33433 affects traefik. Severity is high (CVSS 8.8). 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 a

How urgent is CVE-2026-33433?

Priority 46/100. High severity; Public exploit reference

Software pages

Traefik vulnerabilities

Related CVEs

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CVE-2026-114637 HIGH 8.7 UPGRADE Traefik from v3.2.0 before v3.7.14 contains an authentication bypass vulnerability in the experimental FastPro
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References

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