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BLS Signature "Malleability"

Moderate severity GitHub Reviewed Published Apr 15, 2021 in filecoin-project/lotus • Updated Feb 1, 2023

Package

gomod github.com/filecoin-project/lotus (Go)

Affected versions

< 1.5.0

Patched versions

1.5.0

Description

Impact

  1. BLS signature validation in lotus uses blst library method VerifyCompressed. This method accepts signatures in 2 forms - "serialized", and "compressed", meaning that BLS signatures can be provided as either of 2 unique byte arrays.
  2. Lotus block validation functions perform a uniqueness check on provided blocks. Two blocks are considered distinct if the CIDs of their blockheader do not match. The CID method for blockheader includes the BlockSig of the block.

The result of these issues is that it would be possible to punish miners for valid blocks, as there are two different valid block CIDs available for each block, even though this must be unique.

Patches

By switching from the go based blst bindings over to the bindings in filecoin-ffi, the code paths now ensure that all signatures are compressed by size and the way they are deserialized.
This happened in filecoin-project/lotus#5393

References

References

@dignifiedquire dignifiedquire published to filecoin-project/lotus Apr 15, 2021
Published by the National Vulnerability Database Apr 15, 2021
Reviewed May 20, 2021
Published to the GitHub Advisory Database May 21, 2021
Last updated Feb 1, 2023

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 v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS score

0.135%
(50th percentile)

Weaknesses

CVE ID

CVE-2021-21405

GHSA ID

GHSA-4g52-pqcj-phvh

Source code

No known source code
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