CVE-2020-12399

What it actually does

Timing side-channel in DSA signature generation within NSS allows measurable differences that can leak private key material over repeated observations.

Why it matters to the business

Attackers with local access could recover cryptographic private keys, undermining the confidentiality of signed communications, certificates, or encrypted sessions across affected browsers and email clients.

How an attack unfolds

An attacker with local access to a system running vulnerable NSS triggers repeated DSA signature operations, measures subtle timing variations, and applies statistical analysis to reconstruct the private key bits.

How to fix it

Upgrade affected NSS consumers to Thunderbird 68.9.0 or later, Firefox 77 or later, and Firefox ESR 68.9 or later. For listed OpenEXR packages apply the referenced commits or Debian packages 2.5.4-1 and later.

How to confirm the fix worked

Confirm NSS version meets or exceeds the fixed releases; re-run any available cryptographic timing test suites or verify absence of the original timing delta in signature benchmarks.

Typical attack path

1. Obtain local or user-level access on target system
2. Trigger DSA signature operations via application or library calls
3. Collect high-resolution timing measurements across many signatures
4. Perform offline analysis to extract private key material

How to detect it

Review application logs for unusual volumes of DSA signature operations; inspect process execution patterns involving libnss or Firefox/Thunderbird binaries around the time of suspected local access.

What your security team should do

• Prioritize patching all Firefox, Thunderbird, and NSS-dependent systems within standard patch windows
• Audit cryptographic key material that may have been exposed on systems running vulnerable versions
• Monitor for future side-channel disclosures in cryptographic libraries