Executive Summary

[{'type': 'paragraph', 'content': "CVE-2026-29777 is a vulnerability in Traefik's Kubernetes Gateway provider (versions up to 3.6.9) where a tenant with write access to an HTTPRoute resource can inject malicious rule tokens into Traefik's router rule language. This happens because Traefik interpolates tenant-controlled HTTPRoute header and query parameter match values into its router rules using backtick-delimited string literals without properly escaping or validating these inputs."}, {'type': 'paragraph', 'content': 'Attackers can inject backtick characters and additional rule logic, which alters the parsing of routing rules and bypasses listener hostname constraints designed to isolate tenants in shared gateway deployments. This allows the attacker to redirect traffic intended for victim hostnames to attacker-controlled backends.'}, {'type': 'paragraph', 'content': 'The root cause lies in functions that format rules as Header or Query predicates without escaping special characters, leading to injection of new rule logic. The vulnerability is fixed in Traefik version 3.6.10 by applying injection-safe quoting or rejecting/escaping backticks and special characters.'}] [1]

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Impact Analysis

This vulnerability can have significant impacts in multi-tenant Kubernetes gateway environments. An attacker with write access to HTTPRoute resources can bypass hostname constraints and redirect traffic meant for other tenants to attacker-controlled backends.

Such traffic redirection can lead to credential theft, request forgery, and other downstream attacks, compromising the confidentiality and integrity of data and services.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': "This vulnerability involves injection of backtick-delimited rule tokens into Traefik's router rule language via unsanitized HTTPRoute header or query parameter match values. Detection involves inspecting HTTPRoute resources for suspicious or malformed header or query parameter values containing backticks or unusual rule tokens."}, {'type': 'paragraph', 'content': 'Since the vulnerability requires write access to HTTPRoute resources, you can audit Kubernetes HTTPRoute resources for unexpected or unauthorized modifications, especially looking for backtick characters (`) in header or query parameter match values.'}, {'type': 'paragraph', 'content': 'Commands to help detect this might include:'}, {'type': 'list_item', 'content': "Use kubectl to list HTTPRoute resources and inspect header and query parameter matches for backticks or suspicious patterns: kubectl get httproutes --all-namespaces -o json | jq '.items[].spec.rules[].matches[] | select(.headers != null or .queryParams != null)'"}, {'type': 'list_item', 'content': "Search for backticks in HTTPRoute definitions: kubectl get httproutes --all-namespaces -o yaml | grep -n '\\`'"}, {'type': 'list_item', 'content': 'Monitor Traefik logs for unexpected routing behavior or errors related to rule parsing.'}] [1]

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Mitigation Strategies

The primary mitigation step is to upgrade Traefik to version 3.6.10 or later, where this vulnerability has been fixed.

Until the upgrade can be applied, restrict write access to HTTPRoute resources to trusted users only, as exploitation requires write privileges.

Additionally, review and sanitize HTTPRoute header and query parameter match values to ensure they do not contain backticks or other special characters that could be used for injection.

Implement monitoring and alerting for suspicious changes to HTTPRoute resources and unexpected routing behavior.

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