CVE-2021-21405

Public Exploit
BLS Signature "Malleability"

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.

Category

5.9
CVSS
Severity: Medium
CVSS 3.1 •
CVSS 2.0 •
EPSS 0.17%
Third-Party Advisory github.com Third-Party Advisory github.com Third-Party Advisory github.com
Affected: filecoin-project lotus
Published at:
Updated at:

References

Link Tags
https://github.com/filecoin-project/lotus/security/advisories/GHSA-4g52-pqcj-phvh third party advisory patch
https://github.com/filecoin-project/lotus/pull/5393 third party advisory patch
https://gist.github.com/wadeAlexC/2490d522e81a796af9efcad1686e6754 third party advisory exploit

Frequently Asked Questions

What is the severity of CVE-2021-21405?
CVE-2021-21405 has been scored as a medium severity vulnerability.
How to fix CVE-2021-21405?
To fix CVE-2021-21405, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2021-21405 being actively exploited in the wild?
It is possible that CVE-2021-21405 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-21405?
CVE-2021-21405 affects filecoin-project lotus.
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