nimiq core-rs-albatross up to 1.3.x rebranch behavioral workflow

Summaryinfo

A vulnerability described as critical has been identified in nimiq core-rs-albatross up to 1.3.x. The affected element is the function LightBlockchain::rebranch. Such manipulation leads to behavioral workflow. This vulnerability is documented as CVE-2026-46540. The attack can be executed remotely. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as critical, has been found in nimiq core-rs-albatross up to 1.3.x. Affected by this issue is the function LightBlockchain::rebranch. The manipulation with an unknown input leads to a behavioral workflow vulnerability. Using CWE to declare the problem leads to CWE-841. The product supports a session in which more than one behavior must be performed by an actor, but it does not properly ensure that the actor performs the behaviors in the required sequence. Impacted is integrity, and availability. CVE summarizes:

Nimiq is a Rust implementation of the Nimiq Proof-of-Stake protocol based on the Albatross consensus algorithm. Prior to version 1.4.0, when LightBlockchain::rebranch() adopts a fork chain whose tip is a macro block (checkpoint or election), it only updates self.head but fails to update self.macro_head, self.election_head, self.current_validators, or store the election header in the chain_store. This is in direct contrast with the full Blockchain::rebranch() at blockchain/src/blockchain/push.rs:504-518, which correctly updates all macro/election state when the new head is a macro block. After a rebranch to a macro block, the stale macro_head causes subsequent macro blocks pushed via push() to be verified against the wrong predecessor via verify_macro_successor(&this.macro_head). If the rebranch target was an election block, the stale current_validators causes every subsequent block to fail verify_validators(), completely stalling the light client's chain progression. This issue has been patched in version 1.4.0.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-46540 since 05/14/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit.

Upgrading to version 1.4.0 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying a patch is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• nimiq

Name

• core-rs-albatross

Version

• 1.0
• 1.1
• 1.2
• 1.3

Website

• Product: https://github.com/nimiq/core-rs-albatross/

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