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CometBFT's state syncing validator from malicious node may lead to a chain split

Low severity GitHub Reviewed Published Sep 3, 2024 in cometbft/cometbft • Updated Nov 18, 2024

Package

gomod github.com/cometbft/cometbft (Go)

Affected versions

>= 0.37.0, < 0.37.11
>= 0.38.0, < 0.38.12

Patched versions

0.37.11
0.38.12
gomod github.com/cometbft/cometbft/light (Go)
>= 0.34.0, < 0.34.34
>= 0.37.0, < 0.37.11
>= 0.38.0, < 0.38.12
0.34.34
0.37.11
0.38.12

Description

Name: ASA-2024-009: State syncing validator from malicious node may lead to a chain split
Component: CometBFT
Criticality: Medium (ACMv1.2: I:Moderate; L: Possible)
Affected versions: >= 0.34.0, <= 0.34.33, >=0.37.0, <= 0.37.10, >= 0.38.0, <= 0.38.11

Summary

The state sync protocol retrieves a snapshot of the application and installs it in a fresh node. In order for this node to be ready to run consensus and block sync from the installed snapshot height, we also need to install a valid State in the node, which is the starting state from which it is able to validate new blocks and append them to the blockchain.

The State object used by state sync is computed using the light client protocol, which retrieves information about committed blocks from at least two RPC endpoints. The light client protocol performs several state validations and, in particular, compares the state provided by different RPC endpoints, looking for inconsistencies.

The State object contains, among other fields, a Validators field which stores the current validator set. A validator set is a list of validator addresses, public keys and associated voting powers, one per validator. It also stores, for historical reasons, the state of the proposer selection algorithm, in the form of the ProposerPriority field associated with each Validator.

While the light client is able to validate the ValidatorSet retrieved from RPC endpoints, this validation does not include the ProposerPriority field associated with each Validator. As a result, when state sync adopts RPC endpoints that, for unknown reasons, provide an invalid state of the proposer selection algorithm, the node will not be able to properly run the consensus protocol, as their local view of which validator is the proposer of a given round and height will disagree with the views of the correct validators. If an increasing number of validators state sync using RPC endpoints with invalid states, the network eventually halts.

Patches

Release versions 0.34.34, 0.37.11, and 0.38.12 include a patch to address this issue.

In the patched versions, the light client protocol compares the ProposerPriority fields of the ValidatorSet instances retrieved from the RPC endpoints configured for state sync. If they differ, the computed State object is considered invalid and state sync will fail with an error.

Workarounds

The issue is observed when validators run state sync using RPC nodes that are malicious or report invalid states for the proposer selection algorithm.

It is worth noting that non-malicious nodes running upstream software should never report an invalid state for the proposer selection algorithm. This situation may result from the adoption of nodes with customized code or which had their state, stored in local databases, manually updated.

When the network public's RPC endpoints have an invalid state for the proposer election algorithm, there, new validators should refrain from using state sync for bootstrapping or be sure that they configure for state sync RPC endpoints with a valid state of the proposer election algorithm.

A validator with an invalid state for the proposer selection algorithm will reject most of the proposed blocks and will have the network rejecting blocks it has proposed. It is also possible to manually compare the state of the proposer election algorithm of nodes by comparing the outputs of the /validators?height=_ RPC endpoints. The outputs must fully match, including the ProposerPriority field associated with each validator.

References

This issue was reported to the Cosmos Bug Bounty Program on HackerOne on 12/08/24. If you believe you have found a bug in the Interchain Stack or would like to contribute to the program by reporting a bug, please see https://hackerone.com/cosmos.

If you have questions about Interchain security efforts, please reach out to our official communication channel at security@interchain.io.

For more information about CometBFT, please see https://docs.cometbft.com/.

For more information about the Interchain Foundation’s engagement with Amulet, please see https://github.com/interchainio/security.

References

@ancazamfir ancazamfir published to cometbft/cometbft Sep 3, 2024
Published to the GitHub Advisory Database Sep 3, 2024
Reviewed Sep 3, 2024
Last updated Nov 18, 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 High
Attack Requirements None
Privileges Required None
User interaction Passive
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality Low
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:H/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Weaknesses

No CWEs

CVE ID

No known CVE

GHSA ID

GHSA-g5xx-c4hv-9ccc

Source code

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