CVE-2026-26998: Traefik: unbounded io.ReadAll on auth server response body causes OOM denial of service(DOS)

Severity: medium (CVSS 4.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-05 · updated 2026-06-17
Weakness: CWE-770

Description

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.38 and 3.6.9, there is a potential vulnerability in Traefik managing the ForwardAuth middleware responses. When Traefik is configured to use the ForwardAuth middleware, the response body from the authentication server is read entirely into memory without any size limit. There is no maxResponseBodySize configuration to restrict the amount of data read from the authentication server response. If the authentication server returns an unexpectedly large or unbounded response body, Traefik will allocate unlimited memory, potentially causing an out-of-memory (OOM) condition that crashes the process. This results in a denial of service for all routes served by the affected Traefik instance. This issue has been patched in versions 2.11.38 and 3.6.9.

Affected products

Traefik: before 2.11.38; from 3.0.0 before 3.6.9 — fixed in 2.11.38, 3.6.9

How to fix

Upgrade to a fixed version: Traefik 2.11.38, 3.6.9. Check the vendor advisory for mitigations.

References

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