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Fencer Intel
high 7.5

CVE-2026-26999 json

Traefik: tcp router clears read deadlines before tls forwarding, enabling stalled handshakes (slowloris doS)

published 8mo ago modified 3mo ago also EUVD-2026-9844 , GHSA-xw98-5q62-jx94 , GO-2026-4594

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 49%
public exploits
0
none known

Summary

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 TLS handshake on TCP routers. When Traefik processes a TLS connection on a TCP router, the read deadline used to bound protocol sniffing is cleared before the TLS handshake is completed. When a TLS handshake read error occurs, the code attempts a second handshake with different connection parameters, silently ignoring the initial error. A remote unauthenticated client can exploit this by sending an incomplete TLS record and stopping further data transmission, causing the TLS handshake to stall indefinitely and holding connections open. By opening many such stalled connections in parallel, an attacker can exhaust file descriptors and goroutines, degrading availability of all services on the affected entrypoint. This issue has been patched in versions 2.11.38 and 3.6.9.

Patch / fix

  • go github.com/traefik/traefik/v2 2.11.38
  • go github.com/traefik/traefik/v3 3.6.9
  • Red Hat Red Hat OpenShift Dev Spaces 3.27 1776718585
  • govulncheck-vulndb openSUSE Leap 15.6 0.0.20260317T205859-150000.1.152.1

suse advisories SUSE-SU-2026:1042-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1
  • traefik openSUSE Tumbleweed 3.6.10-1.1
  • traefik2 openSUSE Tumbleweed 2.11.40-1.1

opensuse advisories openSUSE-SU-2026:21483-1openSUSE-SU-2026:10323-1openSUSE-SU-2026:10314-1

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-26999 updated cvss 7.5

github.com/traefik/traefik: Traefik: Denial of Service due to incomplete TLS handshake

  • Red Hat OpenShift Dev Spaces 3.27 devspaces 1776718585
    fixed: vendor fix RHSA-2026:10175
  • Red Hat OpenShift Dev Spaces 3.27 devspaces 1776716842, devspaces 1776717247, devspaces 1776718438, devspaces 1776718450, devspaces 1776718480, devspaces 1776743204, +9 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
8mo ago

Exploit prediction

0.61% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
go github.com/traefik/traefik/v2
<2.11.38
2.11.38
go github.com/traefik/traefik/v3
<3.6.9
3.6.9
go github.com/traefik/traefik
all versions
 no fix listed

Affected products

  • traefik traefik
  • Red Hat Red Hat OpenShift Dev Spaces 3.27

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-772 Missing Release of Resource after Effective Lifetime

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.