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Traefik: kubernetes gateway rule injection via unescaped backticks in HTTPRoute match values

Moderate severity GitHub Reviewed Published Mar 11, 2026 in traefik/traefik • Updated Mar 13, 2026

Package

gomod github.com/traefik/traefik (Go)

Affected versions

<= 1.7.34

Patched versions

None
gomod github.com/traefik/traefik/v2 (Go)
<= 2.11.40
None
gomod github.com/traefik/traefik/v3 (Go)
<= 3.6.9
3.6.10

Description

Summary

There is a potential vulnerability in Traefik's Kubernetes Gateway provider related to rule injection.

A tenant with write access to an HTTPRoute resource can inject backtick-delimited rule tokens into Traefik's router rule language via unsanitized header or query parameter match values. In shared gateway deployments, this can bypass listener hostname constraints and redirect traffic for victim hostnames to attacker-controlled backends.

Patches

For more information

If you have any questions or comments about this advisory, please open an issue.

Original Description

hey Traefik,

repo: https://github.com/traefik/traefik
commit: a4a91344edcdd6276c1b766ca19ee3f0e346480f (as-of 2026-03-02)

traefik's kubernetes gateway provider builds router rules by interpolating HTTPRoute match values into the traefik rule language using backtick-delimited string literals (e.g., Header(name,value), Query(name,value)) without escaping or validation.

because backtick is a delimiter in the rule language, a tenant-controlled backtick can terminate the literal and inject additional rule tokens (for example ) || HostRegexp(.*) || ...). this changes the parsed ast so that an injected OR branch is not gated by the intended Host(...) constraint due to operator precedence, and can result in end-to-end routing hijack (victim host routed to attacker backends).

in shared gateway deployments that rely on gateway API listener hostname constraints to isolate tenants, this can enable cross-tenant routing hijack to attacker-controlled backends.

expected vs actual

expected: provider-generated rules must be injection-safe; tenant-controlled match values must not be able to change the rule parse tree beyond literal argument content, especially across listener hostname-constraint boundaries in shared gateway deployments.

actual: a backtick inside a header/query match value can inject an OR branch into the generated rule, changing the ast root from and to or and enabling hostname-constraint bypass.

severity

HIGH (impact ceiling may reach the top severity tier in shared gateway threat models; end-to-end kubernetes reproduction is recommended to demonstrate cross-tenant routing impact).

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:N = 8.7

cwe: CWE-74 (improper neutralization of special elements in output used by a downstream component)

affected versions

  • confirmed vulnerable at: a4a91344edcdd6276c1b766ca19ee3f0e346480f (pinned commit)
  • release matrix: not yet confirmed (needs version mapping for gateway api provider in v3)

affected code

root cause

the kubernetes gateway provider formats rule strings using backticks as string delimiters:

rules = append(rules, fmt.Sprintf("Header(`%s`,`%s`)", header.Name, header.Value))
rules = append(rules, fmt.Sprintf("Query(`%s`,`%s`)", qp.Name, qp.Value))

if header.Value (or qp.Value) contains a backtick and operator tokens, it can terminate the literal and inject additional rule-language tokens, changing the parse tree.

attacker control

attacker-controlled input is the kubernetes control plane object HTTPRoute in a tenant namespace. the attacker controls:

  1. HTTPRoute.Spec.Rules[].Matches[].Headers[].Value and/or QueryParams[].Value (string)
  2. the payload content, including backticks and rule tokens

impact

in shared gateway setups, this can bypass gateway API listener hostname constraints, causing requests for victim hostnames to be routed to attacker backends. downstream effects can include credential/token capture and request forgery, depending on the workload behind the gateway.

traefik's documentation frames gateway API as providing safer multi-tenant primitives via listener constraints (see https://doc.traefik.io/traefik/security/multi-tenant-kubernetes/). rule injection breaks those constraints when they are relied upon as a boundary.

reproduction (attachment: poc.zip)

attachment includes poc.zip with an integration PoC that:

  • shows canonical behavior where injection changes the parsed ast root to or and routes victim.com to the attacker handler (emits [PROOF_MARKER])
  • shows a negative control using injection-safe quoting (%q) where the ast root remains and and routes victim.com to the victim handler (emits [NC_MARKER])

run canonical:

unzip poc.zip -d poc
cd poc
make canonical

canonical output excerpt:

[CALLSITE_HIT]
[PROOF_MARKER]

run control:

unzip poc.zip -d poc
cd poc
make control

control output excerpt:

[NC_MARKER]

recommended fix

encode rule arguments using injection-safe quoting (for example fmt.Sprintf("Header(%q,%q)", name, value)), or otherwise reject/escape backticks and other rule-language metacharacters before interpolation. add regression tests that include backticks and operator tokens inside header/query match values and assert they cannot change the parse tree.

fix accepted when: tenant-controlled HTTPRoute match values cannot inject operators into the generated rule string and cannot change the resulting parsed ast structure.

[poc.zip](https://github.com/user-attachments/files/25698814/poc.zip)
[PR_DESCRIPTION.md](https://github.com/user-attachments/files/25698815/PR_DESCRIPTION.md)
[attack_scenario.md](https://github.com/user-attachments/files/25698816/attack_scenario.md)

cheers,
Oleh Konko

### References - https://github.com/traefik/traefik/security/advisories/GHSA-8q2w-wr49-whqj - https://github.com/traefik/traefik/releases/tag/v3.6.10 - https://nvd.nist.gov/vuln/detail/CVE-2026-29777
@nmengin nmengin published to traefik/traefik Mar 11, 2026
Published to the GitHub Advisory Database Mar 11, 2026
Reviewed Mar 11, 2026
Published by the National Vulnerability Database Mar 11, 2026
Last updated Mar 13, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required High
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality High
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(2nd percentile)

Weaknesses

Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. Learn more on MITRE.

CVE ID

CVE-2026-29777

GHSA ID

GHSA-8q2w-wr49-whqj

Source code

Credits

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