CVE-2026-18040 Vulnerability Analysis & Exploit Details

CVE-2026-18040
Vulnerability Scoring

Analysis In Progress
Analysis In Progress

Attack Complexity Details

  • Attack Complexity:
    Attack Complexity Analysis In Progress
  • Attack Vector:
    Attack Vector Under Analysis
  • Privileges Required: None
    No authentication is required for exploitation.
  • Scope:
    Impact is confined to the initially vulnerable component.
  • User Interaction: None
    No user interaction is necessary for exploitation.

CVE-2026-18040 Details

Status: Received on 03 Oct 2026, 09:17 UTC

Published on: 03 Oct 2026, 09:17 UTC

CVSS Release:

CVE-2026-18040 Vulnerability Summary

CVE-2026-18040: In Bouncy Castle for Java before 1.86, HQC leaked secret-derived data through two side channels: its GF(2^8) arithmetic used lookup tables indexed by field elements, making the cache line touched a function of the operand, and its fixed-weight support sampler left its duplicate scan as soon as a collision was found and stored accepted positions at a secret index. Both run on secret inputs during encapsulation and decapsulation, and the sampler re-expands the secret key from its seed on every decapsulation, so an attacker able to observe cache behaviour or decapsulation timing can recover information about the HQC private key. The field arithmetic is now table-free and the sampler branch-free within a batch of candidates, with output and randomness consumption unchanged.

Assessing the Risk of CVE-2026-18040

Access Complexity Graph

The exploitability of CVE-2026-18040 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).

Exploitability Analysis for CVE-2026-18040

No exploitability data is available for CVE-2026-18040.

Understanding AC and PR

A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.

Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.

Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.

CVSS Score Breakdown Chart

Above is the CVSS Sub-score Breakdown for CVE-2026-18040, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.

CIA Impact Analysis

Below is the Impact Analysis for CVE-2026-18040, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.

  • Confidentiality: None
    CVE-2026-18040 does not compromise confidentiality.
  • Integrity: None
    CVE-2026-18040 does not impact data integrity.
  • Availability: None
    CVE-2026-18040 does not affect system availability.

CVE-2026-18040 References

External References

CWE Common Weakness Enumeration

CWE-208

CAPEC Common Attack Pattern Enumeration and Classification

  • Cross-Domain Search Timing CAPEC-462 An attacker initiates cross domain HTTP / GET requests and times the server responses. The timing of these responses may leak important information on what is happening on the server. Browser's same origin policy prevents the attacker from directly reading the server responses (in the absence of any other weaknesses), but does not prevent the attacker from timing the responses to requests that the attacker issued cross domain.
  • Application Fingerprinting CAPEC-541 An adversary engages in fingerprinting activities to determine the type or version of an application installed on a remote target.
  • System Footprinting CAPEC-580 An adversary engages in active probing and exploration activities to determine security information about a remote target system. Often times adversaries will rely on remote applications that can be probed for system configurations.

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