Cisco Wi‑Fi boxes are silently stuffing their flash with 5MB of undeletable junk every day

The bug

It has been reported that an updated library in Cisco IOS XE — specifically versions 17.12.4, 17.12.5, 17.12.6 and 17.12.6a — makes access points generate a cnssdaemon.log file that grows by roughly 5MB a day. Cisco warns the file can’t be removed from the command‑line interface, and that the longer an AP runs the affected code the greater the chance it will run out of disk space and fail to download new software images or Access Point Service Packs.

Why it matters

This isn’t just digital clutter. If an access point’s onboard flash fills with the log junk, it may not have room to stage the OS update that would fix the problem — and attempting to update under those conditions could allegedly leave boxes in a dangerous bootloop. In short: the very thing you need to fix the issue might be impossible to install once the device has degraded far enough.

What to do

Cisco’s advisory lists more than 230 affected access point models and includes checks and remediation steps; it has been reported that the vendor recommends moving to IOS XE releases that don’t produce the log, but warns you must ensure there’s enough free flash before attempting the upgrade. Network teams should inventory AP fleets now, run the tests Cisco provides, and plan staged remediations — preferably before flash fills up and the update becomes a high‑stakes rescue mission.

The human angle

If you’ve ever inherited a network and felt like you’d been handed the office key to someone else’s attic, welcome to the party. This is a classic ops problem: small, slow failure that snowballs into a crisis if ignored. Roll up your sleeves, clear the decks, and maybe make a note to check firmware churn next time corporate decides “let’s update a dependency.”

Sources: The Register