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Moderate 60 Bitcoin

fix: warn user before signing raw hashes in message signing (#846)

KX23bc73b3 View source ↗
Public commit record

What the developer wrote

Authored by Odudex

93/100 · Strong
fix: warn user before signing raw hashes in message signing (#846)

Add a warning screen when the input is a raw 32-byte hash or 64-char hex string, alerting the user before signing. This mitigates the risk of an attacker submitting a transaction sighash disguised as a message. Fixes C3 of #843
✓ Specific, descriptive subject✓ Names a concrete action or component✓ Uses a recognizable type or scope✓ Provides detailed explanatory context✓ Links an issue, advisory, or supporting reference
The short version

What changed, and why it matters

This commit adds a warning screen to Krux's message-signing feature when the user is about to sign a raw 32-byte hash or a 64-character hex string. Previously, the device would silently treat such inputs as already-hashed values and sign them directly. Because a Bitcoin transaction's signature hash (sighash) is also a 32-byte value, an attacker could trick a user into signing what looks like a harmless message but is actually a transaction hash, effectively authorizing a transaction. The fix asks the user to confirm before proceeding.

Recommended action

Users should upgrade to a release containing this commit. When signing messages, carefully review the new raw-hash warning and decline unless the source and content are fully trusted. Developers should consider whether raw-hash signing should be further restricted or require an explicit opt-in setting rather than a one-time prompt.

Security signals we found

01

Silent signing of raw 32-byte values allowed transaction sighash spoofing

02

Message signing path treated raw hashes identically to SHA256(message) digests

03

Fix explicitly references 'C3 of #843' as a security concern

04

CHANGELOG.md categorizes the change under 'Security Fixes'

05

No cryptographic validation added; only an interactive warning

Risk score

Why this scored 60/100

Our methodology →
Potential impact 18/30
Exploitability 12/25
Stealth signal 8/15
Affected reach 10/15
Confidence 8/10
Evidence quality 4/5
Human-validated context

Community notes

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