CVE-2020-36843

What it actually does

The EdDSA implementation exhibits signature malleability, permitting generation of distinct valid signatures for a known message and violating the SUF-CMA property.

Why it matters to the business

Organizations using affected email clients on Red Hat Enterprise Linux may face risks to signature-based integrity checks, though prevalence is limited and exploitation remains uncommon.

How an attack unfolds

An attacker obtains a valid signature for a chosen message then derives an alternative valid signature for the identical message, allowing substitution without private key knowledge.

How to fix it

Upgrade affected Thunderbird packages on Red Hat Enterprise Linux 8.4 EUS to version 0:91.7.0-2.el8_4 or later.

How to confirm the fix worked

Confirm package versions match or exceed the fixed releases using the system package manager and re-test signature operations if custom EdDSA usage exists.

Typical attack path

1. Identify a message with an existing valid EdDSA signature
2. Apply malleability transformations to produce a new signature
3. Submit the altered signature in place of the original to bypass verification

How to detect it

Review application logs for duplicate or unexpected signature verifications on identical messages and inspect cryptographic library calls for anomalous behavior.

What your security team should do

• Apply the listed package updates without delay
• Audit any direct dependencies on the vulnerable EdDSA library
• Update vulnerability scanning tools with the corrected package metadata