Summary
Traefik's Kubernetes Ingress NGINX provider may incorrectly merge client certificate authorities when authentication secret names collide after dot-to-dash normalization. An attacker holding a certificate trusted by another host's CA may access a protected host, while legitimate clients for that host may be denied.
Traefik's Kubernetes Ingress NGINX provider may incorrectly merge client certificate authorities when authentication secret names collide after dot-to-dash normalization. An attacker holding a certificate trusted by another host's CA may access a protected host, while legitimate clients for that host may be denied.
Affected context
The issue occurs in Traefik deployments using the Kubernetes Ingress NGINX provider with client certificate authentication. Risk is present when distinct authentication secret names become equivalent after dot-to-dash normalization, causing client CAs associated with different hosts to be combined or selected incorrectly.
The issue occurs in Traefik deployments using the Kubernetes Ingress NGINX provider with client certificate authentication. Risk is present when distinct authentication secret names become equivalent after dot-to-dash normalization, causing client CAs associated with different hosts to be combined or selected incorrectly.
Exploit preconditions
- Attack surface: A host protected by Traefik client certificate authentication
- Required access: A client certificate issued by a CA trusted for another affected host, plus network access to the protected endpoint
- Trigger point: Provider configuration processing and client-CA selection for colliding Kubernetes secret names
- Why exploitation is possible: Name normalization can cause trust material for different hosts to be merged, allowing an unintended CA to authenticate to the target host
- Attack surface: A host protected by Traefik client certificate authentication
- Required access: A client certificate issued by a CA trusted for another affected host, plus network access to the protected endpoint
- Trigger point: Provider configuration processing and client-CA selection for colliding Kubernetes secret names
- Why exploitation is possible: Name normalization can cause trust material for different hosts to be merged, allowing an unintended CA to authenticate to the target host
Why this happens
The vulnerability results from ambiguous identifier normalization in authentication configuration. When secret names containing dots are converted to dash-separated names, distinct references can collide, and the provider may merge their client CAs instead of preserving host-specific trust boundaries. This maps to CWE-287: Improper Authentication, because the resulting trust decision may accept credentials that are not authorized for the requested host.
The vulnerability results from ambiguous identifier normalization in authentication configuration. When secret names containing dots are converted to dash-separated names, distinct references can collide, and the provider may merge their client CAs instead of preserving host-specific trust boundaries. This maps to CWE-287: Improper Authentication, because the resulting trust decision may accept credentials that are not authorized for the requested host.
Potential impact
- An attacker could gain unauthorized access to a host protected by client certificate authentication.
- Cross-host trust contamination could weaken tenant or application isolation.
- Legitimate clients may be rejected or experience authentication failures.
- Security monitoring and access-control assumptions could become unreliable.
- An attacker could gain unauthorized access to a host protected by client certificate authentication.
- Cross-host trust contamination could weaken tenant or application isolation.
- Legitimate clients may be rejected or experience authentication failures.
- Security monitoring and access-control assumptions could become unreliable.
General mitigation guidance
Mitigation generally focuses on preserving unambiguous mappings between hosts, secrets, and trusted certificate authorities.
Defensive patterns include:
- Avoiding secret naming schemes that can become equivalent after normalization.
- Ensuring each protected host has an explicitly isolated client CA configuration.
- Validating normalized names for uniqueness before authentication material is assembled.
- Applying secure-by-default fail-closed behavior when configuration references collide.
- Limiting certificate issuance and trust to the smallest required host or service scope.
- Reviewing existing trust relationships and removing unnecessary cross-host CA acceptance.
Mitigation generally focuses on preserving unambiguous mappings between hosts, secrets, and trusted certificate authorities.
Defensive patterns include:
- Avoiding secret naming schemes that can become equivalent after normalization.
- Ensuring each protected host has an explicitly isolated client CA configuration.
- Validating normalized names for uniqueness before authentication material is assembled.
- Applying secure-by-default fail-closed behavior when configuration references collide.
- Limiting certificate issuance and trust to the smallest required host or service scope.
- Reviewing existing trust relationships and removing unnecessary cross-host CA acceptance.
How teams detect issues like this
Detection can include:
- Static and configuration analysis for secret names that collide after dot-to-dash normalization.
- Code review checks for lossy identifier transformations and map-key overwrites during provider configuration.
- Tests that verify each host accepts only its intended client CA and rejects certificates from other hosts.
- Policy enforcement requiring unique normalized identifiers and explicit host-to-CA mappings.
- Monitoring authentication logs for unexpected cross-host certificate acceptance or sudden legitimate-client rejection.
Automated configuration and code review tools may help identify ambiguous naming and trust-boundary violations.
Detection can include:
- Static and configuration analysis for secret names that collide after dot-to-dash normalization.
- Code review checks for lossy identifier transformations and map-key overwrites during provider configuration.
- Tests that verify each host accepts only its intended client CA and rejects certificates from other hosts.
- Policy enforcement requiring unique normalized identifiers and explicit host-to-CA mappings.
- Monitoring authentication logs for unexpected cross-host certificate acceptance or sudden legitimate-client rejection.
Automated configuration and code review tools may help identify ambiguous naming and trust-boundary violations.
