CVE-2026-88008: traefik advisory

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

What it is

Traefik is an open source HTTP reverse proxy and load balancer. From 2.11.26 until 2.11.57 and 3.7.13, Traefik forwards a client-supplied Connection header requesting Upgrade, the Upgrade: h2c token, and HTTP2-Settings to a shared backend. If the backend accepts h2c and returns 101 Switching Protocols, Traefik enters a raw tunnel and no longer applies routers, BasicAuth, ForwardAuth, IPAllowList, RateLimit, access logging, metrics, or tracing to later HTTP/2 requests, allowing an unauthenticated request through an unprotected route to reach protected paths on the same backend. This issue is fixed in 2.11.57 and 3.7.13.

Description quoted from the CVE record (assigned by GitHub_M, published 2026-09-10).

Weakness: CWE-444: Inconsistent Interpretation of HTTP Requests (‘HTTP Request/Response Smuggling’); CWE-863: Incorrect Authorization

How it can be exploited

Exploitable over the network with low attack complexity only when specific conditions are present needing no privileges and no user interaction. Impact: confidentiality none, integrity none, availability none. CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

CISA assessment (SSVC): CISA has no evidence of exploitation. Automatable: no. Technical impact: partial.

Public exploit evidence (Exploit Observer)

Exploit Observer found 6 code repositories naming this CVE.

Code repositories that name a CVE are often scanners, copies or fakes, and some are malware. Read the code before running anything.

See all 12 references on Exploit Observer

Live scores

EPSS: 0.005
low predicted chance of attack
VEDAS: 0.988
strong exploit evidence
On CISA KEV: Not listed
Detection rule: Nuclei · Suricata

Who is affected

Product	Affected	Not affected
traefik	version >= 2.11.26, < 2.11.57 version >= 3.4.2, < 3.7.13	Not stated

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

How to fix it

No fixed version or vendor advisory is listed in the CVE record yet. Watch the vendor’s security page.

How to detect it

Nuclei template (active check)

Traefik - Authentication Bypass
Traefik forwards a client-supplied Connection header requesting Upgrade, the Upgrade: h2c token and the HTTP2-Settings header to a shared backend. If the backend honours the h2c upgrade and answers 101 Switching Protocols, Traefik enters a raw tunnel and no longer applies routers, BasicAuth, ForwardAuth, IPAllowList, RateLimit, access logging, metrics or tracing to later HTTP/2 requests. An unauthenticated request through an unprotected route can thereby reach protected paths on the same backend. A 101 response carrying Upgrade: h2c proves the backend accepted the cleartext HTTP/2 upgrade that establishes the bypass tunnel. Affected: Traefik 2.11.26 through 2.11.56 and 3.4.2 through 3.7.12.

Name and description quoted from the template, written by VEDAS.

The template sends 1 request (GET /); it decides using status, word matchers. Severity in the template: high. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

bash

nuclei -u https://your-host -t CVE-2026-88008.yaml

Show the template (47 lines)

yaml

id: CVE-2026-88008

info:
  name: "Traefik - Authentication Bypass"
  author: vedas-arpsyndicate
  severity: high
  description: |
    Traefik forwards a client-supplied Connection header requesting Upgrade, the Upgrade: h2c token and the
    HTTP2-Settings header to a shared backend. If the backend honours the h2c upgrade and answers 101 Switching
    Protocols, Traefik enters a raw tunnel and no longer applies routers, BasicAuth, ForwardAuth, IPAllowList,
    RateLimit, access logging, metrics or tracing to later HTTP/2 requests. An unauthenticated request through an
    unprotected route can thereby reach protected paths on the same backend. A 101 response carrying Upgrade: h2c
    proves the backend accepted the cleartext HTTP/2 upgrade that establishes the bypass tunnel.
    Affected: Traefik 2.11.26 through 2.11.56 and 3.4.2 through 3.7.12.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2026-88008&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=traefik&match=exact
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
    cvss-score: 7.4
    cve-id: CVE-2026-88008
    cwe-id: CWE-863
  metadata:
    verified: false
  tags: cve,cve2026,traefik,h2c,auth-bypass,proxy

http:
  - raw:
      - |
        GET / HTTP/1.1
        Host: {{Hostname}}
        Connection: Upgrade, HTTP2-Settings
        Upgrade: h2c
        HTTP2-Settings: AAMAAABkAAQAoAAAAAIAAAAA

    matchers-condition: and
    matchers:
      - type: status
        status:
          - 101

      - type: word
        part: header
        words:
          - "Upgrade"
          - "h2c"
        condition: and

CVE-2026-88008.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2026-88008 Traefik - Authentication Bypass. Add them to your Suricata rule set and reload.

Show the rules

suricata

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2026-88008 Traefik - Authentication Bypass"; flow:established,to_server; http.header; content:"Upgrade|3a 20|h2c"; nocase; fast_pattern; http.method; content:"GET"; classtype:web-application-attack; reference:cve,CVE-2026-88008; reference:url,https://www.exploit.observer/?keyword=CVE-2026-88008&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=traefik&match=exact; sid:1074601; rev:1;)

CVE-2026-88008.rules on GitHub

References

Other references

https://github.com/traefik/traefik/security/advisories/GHSA-w4v4-9rw7-5326 (x_refsource_CONFIRM)
https://github.com/traefik/traefik/pull/13797 (x_refsource_MISC)
https://github.com/traefik/traefik/commit/a277e94664ffc1ce9543df552d3bbf48d4d3b8b3 (x_refsource_MISC)
https://github.com/traefik/traefik/releases/tag/v2.11.57 (x_refsource_MISC)
https://github.com/traefik/traefik/releases/tag/v3.7.13 (x_refsource_MISC)

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.