Juniper Junos OS MACsec key configuration (CKN/CAK): If you configure a MACsec connectivity-association name or key

UnscoredCVE-2018-0021Firmware, BMC & network fabriccurated

Impact

If you configure a MACsec connectivity-association name or key shorter than its full length, Junos silently zero-fills the remainder. A 16-character passphrase you believed was a 256-bit key is 16 characters followed by a long run of zeros, and it falls to dictionary and brute-force attack. MACsec is what protects inter-site and inter-pod links carrying every tenant's traffic, so a recoverable CAK means an attacker with a tap decrypts the lot — and nothing in the config output tells you the key is weak.

Who can reach it

An attacker with a passive tap on the MACsec-protected link who recovers the key offline. No access to the devices is needed.

What to do

Config change, not a patch: reconfigure every MACsec association with the full 64-digit CKN and full 32-digit CAK, generated from a CSPRNG. Rekeying a MACsec link drops it briefly, so do redundant links one at a time. Then audit every MACsec key in the fabric for length — this is the kind of defect that survives for years because the config looks fine.

References

https://nvd.nist.gov/vuln/detail/CVE-2018-0021

This entry is curated: imported from vendor advisories with machine assistance, not yet individually verified. Confirm against your vendor's advisory before acting, and report anything wrong.