Reset the Windows Update cache (rename SoftwareDistribution and catroot2), run DISM and SFC, restart and check for updates again.

What 0x800705B9 actually means

Updates come with metadata files that Windows parses before installing. If they are corrupted on disk or in the cache, parsing fails with 0x800705B9.

Signs of the problem

  • Update fails with 0x800705b9.
  • Defender or cumulative updates affected.

Why 0x800705B9 happens

  • Corrupted update metadata in the cache.
  • Damaged system files.

Fixes to try, in order

  1. Reset the cachePaste the commands below into an admin Command Prompt and restart.
  2. Repair system filesRun DISM and SFC.
  3. Retry and install manually if neededUse the Microsoft Update Catalog for a specific KB.

Command

net stop wuauserv
net stop bits
net stop cryptsvc
ren %systemroot%\SoftwareDistribution SoftwareDistribution.old
ren %systemroot%\System32\catroot2 catroot2.old
net start cryptsvc
net start bits
net start wuauserv

Run each line in an elevated Command Prompt. Renaming these folders only clears the update download cache; Windows rebuilds them.

Check it's fixed: The update installs successfully.

Prevent it from coming back

Avoid interrupting updates and cleaner tools that touch update folders.