CVE-2026-39858
Traefik: Pre-authentication decision bypass due to forwarded alias spoofing in github.com/traefik/traefik
10.0
CRITICAL
CVSS 3.1
EPSS 0.48%
Description
Traefik: Pre-authentication decision bypass due to forwarded alias spoofing in github.com/traefik/traefik
How to fix CVE-2026-39858
To remediate CVE-2026-39858, upgrade the affected package to a fixed version below.
- Go/github.com/traefik/traefik—no fix listed
- —no fix listed
- —upgrade to 2.11.43 or later
- —upgrade to 2.11.43 or later
- —upgrade to 3.7.0-rc.2 or later
- —upgrade to 3.6.14 or later
Is CVE-2026-39858 being exploited?
Low — EPSS is 0.5%, meaning exploitation activity has not been observed at scale.
Affected packages (6)
- from 0, <= 1.7.34
- from 0
- from 0, < 2.11.43
- from 0, < 2.11.43
- >= 3.7.0-ea.1, < 3.7.0-rc.2
- >= 3.0.0-beta1, < 3.6.14, >= 3.7.0-ea.1, < 3.7.0-rc.2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | 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 |
| osv | CVSS 3.1 | CRITICAL10.0 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N |