CVE-2026-29777

Traefik is an HTTP reverse proxy and load balancer. Prior to 3.6.10, 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. This vulnerability is fixed in 3.6.10.

Traefik is an HTTP reverse proxy and load balancer. Prior to 3.6.10, 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. This vulnerability is fixed in 3.6.10.

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

• https://github.com/traefik/traefik/releases/tag/v3.6.10

For more information

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

<details> <summary>Original Description</summary>

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

• pkg/provider/kubernetes/gateway/httproute.go: buildHeaderRules and buildQueryParamRules build Header(%s,%s) / Query(%s,%s) without escaping
• pkg/provider/kubernetes/gateway/grpcroute.go: buildGRPCHeaderRules builds Header(%s,%s) / HeaderRegexp(%s,%s) without escaping
• pkg/provider/kubernetes/knative/kubernetes.go: buildRule builds Header(%s,%s) without escaping
• the generated rule string is parsed by pkg/muxer/http/parser.go (predicate-based rule parser)
• github permalinks (pinned):
  • https://github.com/traefik/traefik/blob/a4a91344edcdd6276c1b766ca19ee3f0e346480f/pkg/provider/kubernetes/gateway/httproute.go#L742
  • https://github.com/traefik/traefik/blob/a4a91344edcdd6276c1b766ca19ee3f0e346480f/pkg/provider/kubernetes/gateway/httproute.go#L761

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…

Traefik is an HTTP reverse proxy and load balancer. Prior to 3.6.10, 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. This vulnerability is fixed in 3.6.10.

Traefik is an HTTP reverse proxy and load balancer. Prior to 3.6.10, 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. This vulnerability is fixed in 3.6.10.

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

• https://github.com/traefik/traefik/releases/tag/v3.6.10

For more information

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

<details> <summary>Original Description</summary>

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

• pkg/provider/kubernetes/gateway/httproute.go: buildHeaderRules and buildQueryParamRules build Header(%s,%s) / Query(%s,%s) without escaping
• pkg/provider/kubernetes/gateway/grpcroute.go: buildGRPCHeaderRules builds Header(%s,%s) / HeaderRegexp(%s,%s) without escaping
• pkg/provider/kubernetes/knative/kubernetes.go: buildRule builds Header(%s,%s) without escaping
• the generated rule string is parsed by pkg/muxer/http/parser.go (predicate-based rule parser)
• github permalinks (pinned):
  • https://github.com/traefik/traefik/blob/a4a91344edcdd6276c1b766ca19ee3f0e346480f/pkg/provider/kubernetes/gateway/httproute.go#L742
  • https://github.com/traefik/traefik/blob/a4a91344edcdd6276c1b766ca19ee3f0e346480f/pkg/provider/kubernetes/gateway/httproute.go#L761

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…