CVE-2016-9243

What it actually does

HKDF key derivation returns an empty byte string when requested output length is shorter than the underlying digest size, silently producing a zero-length key instead of a usable derived secret.

Why it matters to the business

Organizations relying on the affected scanner component risk exposure of container image vulnerabilities or secrets because cryptographic key material may become empty and ineffective, undermining scanning integrity and downstream trust decisions.

How an attack unfolds

An attacker supplies inputs that trigger HKDF with an output length below digest_size; the resulting empty key is used for subsequent cryptographic operations, allowing the attacker to bypass integrity or confidentiality protections that depend on that key.

How to fix it

Upgrade harbor-scanner-trivy-fips (Chainguard) to version 0.31.3-r2 or later; verify the installed package reports the fixed version and restart affected services.

How to confirm the fix worked

Confirm the deployed package version matches or exceeds 0.31.3-r2; run unit tests that exercise HKDF with lengths below digest_size and assert non-empty output; review dependency manifests for any remaining older cryptography versions.

Typical attack path

1. Identify code paths or configurations that invoke HKDF with a length parameter smaller than the algorithm digest size
2. Trigger the vulnerable HKDF call to obtain an empty derived key
3. Use the empty key in encryption, signing, or verification routines to defeat security controls
4. Proceed with further attacks such as reading protected data or injecting malicious content that would normally be rejected

How to detect it

Review application logs for HKDF calls returning empty results or subsequent crypto operations using zero-length keys; inspect dependency manifests and container images for pre-0.31.3-r2 versions of the scanner package.

What your security team should do

• Immediately schedule upgrade of harbor-scanner-trivy-fips to 0.31.3-r2 across all environments
• Audit any custom code or configurations that directly call HKDF and enforce length >= digest_size
• Add dependency scanning to CI pipelines to prevent reintroduction of vulnerable cryptography versions
• Monitor for any scanning failures or anomalous empty-key errors after remediation