CVE-2021-21405: Lotus is an Implementation of the Filecoin protocol written in Go. BLS signature validation in lotus uses blst library method VerifyCompressed. This m...

Description

Lotus is an Implementation of the Filecoin protocol written in Go. 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. 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. 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 https://github.com/filecoin-project/lotus/pull/5393.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability

0.98%

57.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-347

Affected Software

Vendor	Product	Versions
Filecoin	Lotus	< 1.5.0

References

https://gist.github.com/wadeAlexC/2490d522e81a796af9efcad1686e6754Exploit, Third Party Advisory
https://github.com/filecoin-project/lotus/pull/5393Patch, Third Party Advisory
https://github.com/filecoin-project/lotus/security/advisories/GHSA-4g52-pqcj-phvhPatch, Third Party Advisory
https://gist.github.com/wadeAlexC/2490d522e81a796af9efcad1686e6754Exploit, Third Party Advisory
https://github.com/filecoin-project/lotus/pull/5393Patch, Third Party Advisory
https://github.com/filecoin-project/lotus/security/advisories/GHSA-4g52-pqcj-phvhPatch, Third Party Advisory

Timeline

Published: Apr 15, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21405?

Lotus is an Implementation of the Filecoin protocol written in Go. 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. 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. 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 https://github.com/filecoin-project/lotus/pull/5393.

How severe is CVE-2021-21405?

CVE-2021-21405 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.98% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21405?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.