CVE-2026-88879: Traefik is an HTTP reverse proxy and load balancer

Routine

HIGH 8.2REMOTEUPGRADE

CVE-2026-88879 is a high-severity flaw (CVSS 8.2) 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. In Traefik v1.x, v2.x through v2.11.55, and v3.0.0 through v3.7.11, header names are canonicalized only on dashes, so X-Auth-User, X_Auth_User and X.Auth.User are treated as three distinct headers by Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX and others) collapse them into a single variable. A client can therefore smuggle a dot-form alias of a hea

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	8.2 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 78%)
CISA exploited list	No
Weakness	CWE-290
Published	2026-09-10
Last modified	2026-10-08

Publisher (CNA): VulnCheck · Vendor: traefik

Last updated 2026-10-08 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-10 14:17 UTCPublished CVE record published
2026-10-08 16:17 UTCUpdated Record last modified

traefik traefik UPGRADE

Affected: >= 1.0 and < 2.11.56 · >= 3.0.0 and < 3.7.12

Fixed in: 2.11.56, 3.7.12

Safe to downgrade to: a release before 1.0

1. Check installed version

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

2. UPGRADE to 2.11.56 (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 1.0 (Debian / Ubuntu)

apt-cache madison traefik sudo apt install traefik=<VERSION_BEFORE_1.0> 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_1.0> 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-2026-88879?

traefik: upgrade to 2.11.56, 3.7.12. Exact commands for each OS are on this page.

Is CVE-2026-88879 being exploited?

CVE-2026-88879 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-2026-88879 affect?

CVE-2026-88879 affects traefik. Severity is high (CVSS 8.2). Traefik is an HTTP reverse proxy and load balancer. In Traefik v1.x, v2.x through v2.11.55, and v3.0.0 through v3.7.11, header names are canonicalized only on dashes, so X-Auth-User, X_Auth_User and X.Auth.User are treated as three distinct

How urgent is CVE-2026-88879?

Priority 39/100. High severity; Remotely exploitable, no login, no user action

Software pages

nginx vulnerabilities · PHP vulnerabilities · Traefik vulnerabilities

Related CVEs

CVE-2026-65600 MEDIUM 5.3 UPGRADE Traefik versions <= v2.11.51, >= v3.6.0 <= v3.6.22, and >= v3.7.0 <= v3.7.6 contain an authentication bypass v
CVE-2026-112778 HIGH 8.8 UPGRADE Traefik before 2.11.46, 3.x before 3.6.17, and 3.7.0 lack namespace validation for Ingress and Service annotat
CVE-2026-88878 MEDIUM 5.3 UPGRADE Traefik is an HTTP reverse proxy and load balancer
CVE-2026-88877 CRITICAL 9.8 UPGRADE Traefik is a HTTP reverse proxy and load balancer
CVE-2026-85597 CRITICAL 9.1 UPGRADE Traefik before v2.11.55 and v3.0.0 through v3.7.10 contain a TLS option conflict resolution vulnerability that

References

← Back to latest CVEs