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Hidden volume quick format weakens plausible deniability

Moderate
idrassi published GHSA-jjcr-75w7-58jp Jun 5, 2026

Package

VeraCrypt

Affected versions

between 1.26.6 and 1.26.28

Patched versions

1.26.29

Description

Summary

When creating a file-hosted hidden volume, VeraCrypt can write raw zeroed sectors directly into the container file. These sectors can appear at predictable 128 MiB intervals inside an area that should look like random ciphertext. No encrypted content is compromised, and VeraCrypt's encryption itself is not weakened, but the zeroed sectors can weaken plausible deniability protections via a deterministic pattern.

Details

Hidden volume creation forces volParams->quickFormat = TRUE in src/Common/Format.c. For file-hosted volumes, FormatNoFs() and FormatFat() receive quickFormat == TRUE and bDevice == FALSE.

In the quick-format file-container branches, both functions seek through the target and call WriteFile() directly with a zeroed sector buffer:

  • src/Common/Format.c: FormatNoFs() quick-format branch
  • src/Common/Fat.c: FormatFat() quick-format branch

This 128 MiB zero-sector write behavior was added in 579ce2fd31f01b0befba947ed863ed1d5e4be3f0 to improve Windows quick-format progress reporting and force allocation of each 128 MiB chunk in file containers.

These direct writes do not use the normal formatting path, where buffered sectors are transformed by EncryptDataUnits() before being written. As a result, hidden file-hosted volumes can contain raw zero sectors in the hidden volume data area.

PoC

  1. Create a file-hosted outer volume.
  2. Create a hidden volume inside it with a size greater than 128 MiB.
  3. In the hidden volume format options, choose either no filesystem, which reaches FormatNoFs(), or FAT, which reaches FormatFat().
  4. Complete hidden volume creation. Hidden volumes force quick format internally; no separate quick-format selection is required.
  5. Inspect the host file at offsets within the hidden volume data area.
  6. Observe zeroed sectors at predictable 128 MiB intervals written by the quick-format file-container path.

Impact

This is a hidden-volume deniability weakness / security feature bypass. Users creating file-hosted hidden volumes are impacted because the host file may contain deterministic plaintext markers where random-looking encrypted data is expected. The issue does not disclose hidden volume contents or reduce encryption strength, but it can create forensic evidence inconsistent with VeraCrypt's hidden-volume threat model.

Disclaimer: This vulnerability was identified with assistance from OpenAI Codex Security using GPT-5.5 xhigh, then verified through multiple iterations and reviewed with Claude Opus 4.8 Max. All AI review used flagship models at the highest reasoning settings.

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction Active
Vulnerable System Impact Metrics
Confidentiality Low
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

CVE ID

CVE-2026-54073

Weaknesses

No CWEs

Credits