CVE-2026-9648: CVE-2026-9648

Synopsis

An authentication bypass vulnerability in the crypton-x509-validation Haskell library (crypton-certificate versions before 1.9.1) allows TLS clients to silently accept certificates whose Subject Alternative Names fall outside a sub-CA's NameConstraints. The flaw is reachable over the network with no authentication required and no user interaction needed. Successful exploitation lets an attacker who has compromised a name-constrained sub-CA impersonate arbitrary domains, enabling man-in-the-middle attacks against encrypted traffic. A patched-image rebuild at version 1.9.1 is available on HarborGuard for environments running an affected version.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the vulnerable TLS client over the network; the library is exposed whenever an application initiates or validates TLS connections to remote endpoints.

• AuthenticationNot required

  No credentials or account are needed; the attacker only needs to present a crafted certificate during the TLS handshake.

• Victim interactionNot required

  No user action is required; exploitation occurs passively during normal TLS connection establishment by the affected library.

• Attack complexityDetail

  Attack complexity is low; the exploit is reliable and condition-free once the attacker controls a name-constrained sub-CA or can position themselves to present a crafted certificate.

Blast Radius

• Attacker impersonates arbitrary domains beyond the sub-CA's permitted scope, intercepting or reading plaintext from TLS-protected connections the client believes are authenticated.
• Attacker modifies in-transit data exchanged over those impersonated TLS sessions, injecting commands, responses, or payloads without detection by the client.
• Trust anchors and certificate pinning logic built on top of the affected library are bypassed, undermining downstream security controls that rely on correct NameConstraints enforcement.