How severe is CVE-2026-33433?

CVE-2026-33433 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-33433 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33433?

CVE-2026-33433 primarily affects Traefik. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-33433?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-33433 have an EU (EUVD) identifier?

Yes. CVE-2026-33433 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16616.

When was CVE-2026-33433 published?

CVE-2026-33433 was published on 2026-03-27 and last updated on 2026-06-30.

CVE-2026-33433

CVE-2026-33433 is a high-severity vulnerability in Traefik with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-290.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v4: 5.1
EPSS exploit prediction: 0% (37th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-16616
Weakness: CWE-290
Affected product: Traefik
Published: 2026-03-27
Last modified: 2026-06-30

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.

Frequently asked questions

What is CVE-2026-33433?: 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.
How severe is CVE-2026-33433?: CVE-2026-33433 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-33433 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33433?: CVE-2026-33433 primarily affects Traefik. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-33433?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-33433 have an EU (EUVD) identifier?: Yes. CVE-2026-33433 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16616.
When was CVE-2026-33433 published?: CVE-2026-33433 was published on 2026-03-27 and last updated on 2026-06-30.

References

Affected products (3)

cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*
cpe:2.3:a:traefik:traefik:3.7.0:ea1:*:*:*:*:*:*
cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:*

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