CVE-2021-21405Public exploitNetwork attack vector

Miner punishment via malleable BLS signatures

Published Apr 15, 2021 · Updated Aug 3, 2024

BLS signature malleability in Filecoin Lotus before 1.5.0 allows remote attackers to create two valid block-header CIDs for one block. Block validation includes BlockSig in each header CID while VerifyCompressed accepts serialized and compressed encodings of the same valid signature. Unauthenticated network access is sufficient to submit the alternate encoding, causing honest miners to be punished for valid blocks.

CVSS severity5.9
Medium
EPSS probability0.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

BLS signature malleability in Filecoin Lotus before 1.5.0 allows remote attackers to create two valid block-header CIDs for one block. Block validation includes BlockSig in each header CID while VerifyCompressed accepts serialized and compressed encodings of the same valid signature. Unauthenticated network access is sufficient to submit the alternate encoding, causing honest miners to be punished for valid blocks.

The record

CVE
CVE-2021-21405
Published
Apr 15, 2021
Updated
Aug 3, 2024
Vendor
Filecoin
Product
Lotus
Classifications
CWE-347
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.5.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Filecoin · Lotusversion=< 1.5.0

Published CVSS scores

5.9GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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