Cisco Wi-Fi boxes are filling their disks with 5MB of undeletable data every day
- Reference: 1776400546
- News link: https://www.theregister.co.uk/2026/04/17/cisco_wifi_ap_useless_data/
- Source link:
The networking giant revealed the mess earlier this week in an [1]advisory that warns “Certain Cisco Access Points (APs) may fail to download new software images or Access Point Service Packs.”
The reason for the mess is an updated library in Cisco IOS XE – specifically versions 17.12.4, 17.12.5, 17.12.6, and 17.12.6a – which sees access points generate a log file named cnssdaemon.log .
[2]
Cisco says that file grows by 5MB every day and can’t be deleted from the command line interface.
[3]
[4]
“The longer an AP runs the affected software, the higher the probability that a software download will fail due to insufficient disk space,” Cisco warns.
Moving to a version of IOS XE that doesn’t write the log file is the obvious fix, but Cisco warns it’s not that simple because if your Wi-Fi box has filled its flash with junk, it may not have enough internal storage space to hold the updated OS.
[5]
If that’s the case, Cisco warns you could end up with a bootloop.
[6]Cisco turns to titanium spoons and sand dunes to build a better … box?
[7]Cisco set to release home-brew hypervisor as a VMware alternative
[8]Cisco hikes prices to cover memory cost rises, says you don’t much care
[9]Cisco challenges Broadcom, Nvidia with a 102.4T switch of its own
Cisco’s advisory therefore includes a procedure to test for the presence of the offending IOS XE releases, and instructions on how to sort things out.
The advisory also lists over 230 models of Cisco access points that run the rotten versions of IOS XE.
The Register is certain all readers running Cisco Wi-Fi kit will have accurate and recently-updated inventories of your access point fleets and can therefore swiftly identify and remediate hardware that needs attention. Those of you who don’t have that info at hand doubtless inherited a mess from a slovenly predecessor and now get to be the hero who tidies things up.
While you’re at it, you may also wish to consider another issue Cisco identified which [10]relates to voicemail synching issues that may arise once Microsoft [11]shuts down Exchange Web Services. ®
Get our [12]Tech Resources
[1] https://www.cisco.com/c/en/us/support/docs/field-notices/743/fn74383.html
[2] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_onprem/networks&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=2&c=2aeIEycKcm2ngoCxtez3u2AAAAUM&t=ct%3Dns%26unitnum%3D2%26raptor%3Dcondor%26pos%3Dtop%26test%3D0
[3] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_onprem/networks&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=4&c=44aeIEycKcm2ngoCxtez3u2AAAAUM&t=ct%3Dns%26unitnum%3D4%26raptor%3Dfalcon%26pos%3Dmid%26test%3D0
[4] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_onprem/networks&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=3&c=33aeIEycKcm2ngoCxtez3u2AAAAUM&t=ct%3Dns%26unitnum%3D3%26raptor%3Deagle%26pos%3Dmid%26test%3D0
[5] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_onprem/networks&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=4&c=44aeIEycKcm2ngoCxtez3u2AAAAUM&t=ct%3Dns%26unitnum%3D4%26raptor%3Dfalcon%26pos%3Dmid%26test%3D0
[6] https://www.theregister.com/2026/02/24/cisco_everpure_brand_design/
[7] https://www.theregister.com/2026/02/16/cisco_nfvis_for_uc_hypervisor/
[8] https://www.theregister.com/2026/02/12/cisco_q2_2026/
[9] https://www.theregister.com/2026/02/10/cisco_challenges_broadcom_nvidia_switch_chips/
[10] https://www.cisco.com/c/en/us/support/docs/field-notices/743/fn74365.html
[11] https://www.theregister.com/2026/02/06/microsoft_ews_shutdown/
[12] https://whitepapers.theregister.com/
Re: Ah, Cisco
Yes, with friends like them, who needs enemies?
How do you screw up that badly?
Clearly, when there's limited flash storage, you have log rotation once log files hit a few MiB in size and you ensure the router can boot and can clear log files even when out of storage.
Re: How do you screw up that badly?
We have shipped code to clients with debug logs writing to files in /tmp - fortunately not in a production build, but if it happens to the best of us (he says modestly) it can definitely happen to Cisco
Re: How do you screw up that badly?
Many years ago:
I worked on a site that had an identical machine image on all machines. I updated it only rarely, usually to add new local software into the base install. I once built a new machine image and, in the process, inadvertantly left behind a 300Mb ZIP file in the "Public" user download folder, the installer for the software I'd put into the image.
After some months, I picked up that the servers were running out of disk space. Did a WinDirStat across the entire network storage.
Every user profile (this was in the days of roaming profiles) had picked up this ZIP file. (I did work out why in the end but I can't remember the details - I presume because when there wasn't an existing network profile for the user, it would copy the existing "Default User" profile as a template and suck in this ZIP file, but how it had picked up that file, I can't remember). And we'd just purged people's profiles to help with a site-wide OS change / upgrade.
So every user was pushing back a 300Mb ZIP file to their roaming profile, and then downloading it again when they logged in anywhere. And because all the machines were identically imaged, they were all doing this.
I was still finding people, a year later, with that ZIP file in their profile because of various machines that had been missed, and users logging in in multiple locations and just locking their machine instead of logging off, so they were constantly putting that file back into their roaming profile when those machines finally logged off.
Doesn't sound much but when you have nearly 1000 users, that's 300Gb, which was about 1/3rd of our total network storage at the time.
I mean, credit to my networking and storage as it barely affected logon/logoff times even on a fresh user, and I hadn't even noticed until the disks on the server started filling up.
But what a pain resulted from that one simple mistake.
Re: How do you screw up that badly?
That isn't comparable, considering that it won't brick the computer, as /tmp/ gets wiped on poweroff or on boot, on decent OS's.
For a router with NAND flash, unless the plan is to kill the flash in short order, /tmp/ or logging locations should be assigned to a few MiB of compressed RAMdisk with log rotation and if the logs needs to be saved, only committed to flash every few hours (or a configurable time), or on reboot.
cisco
Why would anyone still be using cisco gear? They seem to have a major issue every other week and it's usually stupid mistakes that you wouldn't expect from a trainee programmer.
Re: cisco
The same reason why people still keep using microslop - it's popular, so it must be good.
Ah, Cisco
Thank goodness we banned that awful Chinese threat from our networks, right ?
Dealing with one threat is enough.