CVE-2026-108266 in rustls
Summary
by MITRE • 10/10/2026
Privasys rustls is a maintained fork of the rustls TLS library that adds RA-TLS challenge and channel-binding support. Prior to privasys-v0.8.1, the fork emitted RA-TLS challenge certificates whose quote ReportData was bound to the certificate public key and client nonce but not to the active TLS session. An attacker who obtained an enclave TLS private key could relay a genuine quote onto another connection, causing a relying party to accept an attacker-terminated connection as the attested enclave. This issue is fixed in privasys-v0.8.1.
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Analysis
by VulDB Data Team • 10/10/2026
The vulnerability identified in Privasys rustls prior to version 0.8.1 represents a critical flaw in the implementation of Remote Attestation Transport Layer Security, commonly referred to as RA-TLS. This protocol extension is designed to establish secure communication channels with remote enclaves by verifying their integrity and identity through cryptographic proofs known as quotes. The core issue stems from an incomplete binding mechanism within the certificate generation process. Specifically, while the quote ReportData was correctly bound to the certificate public key and the client nonce, it failed to include a binding to the active TLS session parameters. This omission creates a significant gap in the chain of trust, allowing for sophisticated relay attacks that undermine the fundamental security guarantees provided by hardware-based attestation mechanisms.
From a technical perspective, the flaw allows an attacker who has compromised or obtained the private key associated with an enclave's certificate to perform a man-in-the-middle attack without needing to break the underlying cryptographic algorithms. By intercepting and relaying a genuine quote from one TLS connection to another, the attacker can trick the relying party into accepting their own terminated connection as if it were the legitimate attested enclave. The reliance on only the client nonce is insufficient because nonces are typically short-lived or reusable in certain contexts, whereas session-specific data such as handshake hashes provide unique context that prevents replay and relay attacks across different connections. This lack of session binding means that the cryptographic proof does not uniquely identify the specific TLS session being established, rendering the attestation process vulnerable to substitution attacks where valid credentials from one session are applied to a maliciously controlled connection in another.
The operational impact of this vulnerability is severe for any system relying on RA-TLS for secure enclave communication. An attacker can effectively impersonate a trusted remote service by relaying authentic quotes, thereby bypassing integrity checks that are supposed to ensure the code running within the enclave has not been tampered with. This compromises confidentiality and integrity, as sensitive data may be exfiltrated or manipulated under the guise of a legitimate connection. The attack vector aligns closely with CWE-295 Improper Certificate Validation and CWE-384 Session Fixation concepts adapted for TLS contexts, specifically highlighting failures in binding cryptographic proofs to session context. In terms of MITRE ATT&CK techniques, this vulnerability facilitates T1078 Valid Accounts through the misuse of legitimate enclave credentials and supports lateral movement or initial access via relay attacks similar to those described under credential replay scenarios.
To mitigate this risk, organizations must immediately upgrade Privasys rustls to version 0.8.1 or later, where the binding logic has been corrected to include active TLS session data in the quote ReportData. This ensures that each attestation is uniquely tied to its specific connection context, preventing relaying attacks across different sessions. Additionally, developers should implement strict certificate validation policies and monitor for anomalous patterns indicative of relay attempts, such as repeated connections from unexpected sources using identical nonces but varying session parameters. Regular security audits focusing on TLS implementation details and adherence to industry standards like NIST SP 800-193 for platform firmware attestation can further strengthen defenses against these types of protocol-level exploits.