CVE-2016-6489

What it actually does

The vulnerability in Nettle's RSA and DSA decryption routines allows cache side-channel attacks that can leak private key material through observable timing or cache access patterns during cryptographic operations.

Why it matters to the business

Recovery of private keys could allow attackers to decrypt protected communications or data, leading to loss of confidentiality for sensitive information and potential compromise of authentication mechanisms.

How an attack unfolds

An attacker with local or co-located access observes cache behavior while the target performs RSA or DSA decryption, collecting side-channel data over repeated operations to reconstruct bits of the private key.

How to fix it

Apply the patch from commit c16fa4f2ad19908a47c63d8fa436a1178438c7e7 in the affected Linux kernel git repository to address the side-channel leakage in Nettle's decryption code.

How to confirm the fix worked

Confirm the fix commit is present in the source tree or verify that Nettle-based cryptographic components have been rebuilt with the updated implementation; test decryption operations for consistent timing behavior.

Typical attack path

1. Gain access to observe CPU cache activity on the target system
2. Trigger or intercept RSA/DSA decryption operations
3. Measure cache hits, misses, or timing variations during key-dependent computations
4. Aggregate observations across multiple decryptions to recover private key bits
5. Reconstruct and validate the full private key

How to detect it

Side-channel exploitation leaves minimal artifacts; examine system performance logs, cryptographic library usage, and any unusual patterns in decryption latency or cache-related monitoring tools for signs of targeted observation.

What your security team should do

• Prioritize patching the affected cryptographic library across all systems
• Review and rotate any RSA or DSA keys that may have been used in vulnerable environments
• Implement constant-time cryptographic primitives where possible to reduce side-channel exposure