CVE-2021-21405 BLS Signature "Malleability"

What is CVE-2021-21405?

CVE-2021-21405 is a medium-severity vulnerability in filecoin-project lotus, published on 15 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-347

Which versions are affected by CVE-2021-21405?

3 open source packages ship an affected version, including github.com/filecoin-project/lotus. It affects 1 product.

Products include Filecoin Lotus.

How do I fix CVE-2021-21405?

Upgrade github.com/filecoin-project/lotus to 1.5.0 or later.

Is CVE-2021-21405 being exploited?

There is no known exploitation of CVE-2021-21405 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-4g52-pqcj-phvh, GO-2022-0905.