CVE-2016-1938

What it actually does

Improper division in s_mp_div within the MPI library leads to incorrect results from mp_div and mp_exptmod, weakening cryptographic operations such as modular arithmetic used in key handling and signature processes.

Why it matters to the business

Attackers may bypass encryption protections in affected systems, increasing risk of data exposure or unauthorized access across widely deployed network security components.

How an attack unfolds

An attacker supplies crafted inputs that invoke the flawed division during cryptographic routines, exploiting incorrect modular results to undermine protection mechanisms without needing authentication.

How to fix it

Upgrade Mozilla NSS to 3.21 or newer and Firefox to 44.0 or newer; rebuild or redeploy any dependent packages to incorporate the corrected MPI implementation.

How to confirm the fix worked

Verify installed NSS and Firefox versions against the fixed releases; perform regression tests on cryptographic functions to confirm correct division behavior.

Typical attack path

1. Locate services or clients relying on vulnerable NSS versions
2. Trigger cryptographic operations that call mp_div or mp_exptmod
3. Leverage erroneous division outcomes to weaken or defeat crypto protections
4. Proceed with follow-on attacks against now-exposed communications or data

How to detect it

Search application and system logs for cryptographic operation failures or version strings indicating pre-3.21 NSS; inspect process listings and package inventories for vulnerable library instances.

What your security team should do

• Prioritize patching NSS and Firefox across all environments due to widespread use in cryptographic libraries
• Audit dependent open-source distributions for bundled vulnerable versions
• Review cryptographic usage logs for anomalies after patching