Skip to content

biscuit-auth vulnerable to public key confusion in third party block

Low severity GitHub Reviewed Published Jul 31, 2024 in biscuit-auth/biscuit-rust • Updated Aug 5, 2024

Package

cargo biscuit-auth (Rust)

Affected versions

>= 4.0.0, < 5.0.0

Patched versions

5.0.0

Description

Third-party blocks can be generated without transferring the whole token to the third-party authority. Instead, a ThirdPartyBlock request can be sent, providing only the necessary info to generate a third-party block and to sign it:

  • the public key of the previous block (used in the signature)
  • the public keys part of the token symbol table (for public key interning in datalog expressions)

A third-part block request forged by a malicious user can trick the third-party authority into generating datalog trusting the wrong keypair.

Consider the following example (nominal case)

  • Authority A emits the following token: check if thirdparty("b") trusting ${pubkeyB}
  • The well-behaving holder then generates a third-party block request based on the token and sends it to third-party authority B
  • Third-party B generates the following third-party block thirdparty("b"); check if thirdparty("c") trusting ${pubkeyC}
  • The token holder now must obtain a third-party block from third party C to be able to use the token

Now, with a malicious user:

  • Authority A emits the following token: check if thirdparty("b") trusting ${pubkeyB}
  • The holder then attenuates the token with the following third party block thirdparty("c"), signed with a keypair pubkeyD, privkeyD) they generate
  • The holder then generates a third-party block request based on this token, but alter the ThirdPartyBlockRequest publicKeys field and replace pubkeyD with pubkeyC
  • Third-party B generates the following third-party block thirdparty("b"); check if thirdparty("c") trusting ${pubkeyC}
  • Due to the altered symbol table, the actual meaning of the block is thirdparty("b"); check if thirdparty("c") trusting ${pubkeyD}
  • The attacker can now use the token without obtaining a third-party block from C.

Impact

Tokens with third-party blocks containing trusted annotations generated through a third party block request

References

@Geal Geal published to biscuit-auth/biscuit-rust Jul 31, 2024
Published to the GitHub Advisory Database Jul 31, 2024
Reviewed Jul 31, 2024
Published by the National Vulnerability Database Aug 1, 2024
Last updated Aug 5, 2024

Severity

Low

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 Network
Attack Complexity Low
Attack Requirements Present
Privileges Required High
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity Low
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:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

EPSS score

0.045%
(15th percentile)

Weaknesses

CVE ID

CVE-2024-41949

GHSA ID

GHSA-p9w4-585h-g3c7

Source code

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.