CVE-2026-87737 in mirage-crypto-ec
Summary
by MITRE • 09/09/2026
An issue was discovered in the mirage-crypto-ec package before 2.4.0 for OCaml. There is a timing side channel for NIST elliptic-curve scalar multiplication: the time required for a lookup can depend on a secret.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified within the mirage-crypto-ec library prior to version 2.4.0 represents a critical implementation flaw in the cryptographic primitives used for secure communications, specifically affecting NIST elliptic curve scalar multiplication operations. As a widely utilized OCaml-based cryptography package often employed in systems requiring high assurance and formal verification, such as those built on the Mirage unikernel framework, this library plays a pivotal role in establishing secure channels via protocols like TLS or SSH that rely on Elliptic Curve Diffie-Hellman key exchanges. The core of the issue lies in the algorithmic implementation of scalar multiplication, where the computational time required to perform specific lookup operations within the underlying data structures exhibits variance based on secret values derived from private keys. This timing side channel arises because certain branches or memory access patterns execute faster when processing specific bits of the secret scalar compared to others, creating a measurable discrepancy in execution duration that can be exploited by an attacker with network-level visibility or local process monitoring capabilities.
From a technical perspective, this flaw aligns directly with CWE-208, which describes observable timing discrepancies as a source of information leakage, and is further categorized under CWE-367 for time-of-check to time-of-use issues in the context of cryptographic operations where constant-time execution is mandated but not achieved. The vulnerability allows an adversary to perform a differential power analysis or simple timing attack by sending multiple requests with varying inputs and measuring the response times with high precision. By statistically analyzing these temporal differences, it becomes possible to reconstruct bits of the private key used in the scalar multiplication process. This type of attack does not require breaking the underlying mathematical hardness assumptions of elliptic curve cryptography but rather exploits the physical or logical execution characteristics of the software implementation itself. In environments where side-channel resistance is a security requirement, such as smart cards, hardware security modules, or high-security server applications, this lack of constant-time behavior constitutes a severe deviation from best practices defined by standards like NIST SP 800-57 and BSI TR-02102.
The operational impact of this vulnerability is significant, particularly for services that handle sensitive data exchange using EC-based key agreements. If an attacker successfully exploits the timing side channel, they can recover the long-term private keys associated with the elliptic curves in use. The compromise of these keys leads to a complete breakdown of confidentiality and integrity guarantees provided by the cryptographic protocol. Attackers could decrypt past recorded traffic if forward secrecy is not properly implemented or configured, although EC-DH typically provides perfect forward secrecy for session keys, the exposure of static private keys allows an attacker to impersonate the server in future connections or potentially derive shared secrets for new sessions involving that compromised key pair. This undermines trust in the entire security infrastructure relying on mirage-crypto-ec and necessitates immediate remediation to prevent unauthorized access, data exfiltration, and man-in-the-middle attacks against protected communications channels.
Mitigation strategies must prioritize both software updates and architectural adjustments. The primary defense is upgrading the mirage-crypto-ec package to version 2.4.0 or later, where the developers have implemented constant-time algorithms for scalar multiplication that eliminate data-dependent timing variations. This involves ensuring that all branches in the code execute regardless of secret values and that memory access patterns do not reveal information about the private key through cache behavior or execution time. Additionally, organizations should audit their dependency trees to ensure no other components introduce similar side-channel vulnerabilities. Implementing network-level latency normalization techniques can provide a secondary layer of defense by adding random delays to responses, although this is generally considered less effective than fixing the root cause in the cryptographic implementation itself. Regular security assessments and penetration testing focused on timing attacks should be incorporated into the development lifecycle for any system utilizing elliptic curve cryptography to ensure ongoing resilience against side-channel exploitation techniques documented in MITRE ATT&CK technique T1530, which covers data from cloud storage or internal systems via exfiltration methods that may include cryptographic key theft.