NEURLFilter / SimpleURLFilter: neagent fails to open URL prefilter mmap file with errno 13 Permission denied

I am testing NEURLFilter on macOS using the SimpleURLFilter sample, and I am seeing a failure from neagent while it is saving the local URL prefilter Bloom filter to its mmap file.

The relevant log is:

neagent	+[NEBloomFilter mmapToFile:data:dataLength:numberOfBits:numberOfHashes:murmurSeed:tag:]: NEBloomFilter - failed to open mmap file /private/var/db/urlPrefilter/com.apple.networkextension.url-prefilter-data.temp.com.example.apple-samplecode.SimpleURLFilterTC3Q7MAJXF <errno 13 - Permission denied>
neagent	<NEAgentURLFilterExtension: 0xc8ce64280>: -[NEAgentURLFilterExtension startURLFilter]_block_invoke - Failed to save first fetch of pre-filter data

Environment:

• macOS: 26.5.1 (25F80)
• Xcode: 26.5 (17F42)
• Platform: macOS
• Signing type: Apple Development (automatically manage signing)

What I am doing:

1. Build and run the containing app.
2. Save and enable the NEURLFilterManager configuration.
3. The URL filter provider starts.
4. The provider's prefilter code is reached.
5. neagent logs the mmap failure above while trying to open a temporary file under /private/var/db/urlPrefilter.

Expected result:

neagent should be able to create or open its system-managed URL prefilter cache / mmap file under /private/var/db/urlPrefilter, and the local Bloom filter should be loaded successfully.

Actual result:

neagent fails to open the temporary mmap file with errno 13 Permission denied:

/private/var/db/urlPrefilter/com.apple.networkextension.url-prefilter-data.temp.<bundle/team-specific suffix>

I am not manually creating, modifying, or chmod/chown-ing /private/var/db/urlPrefilter or anything inside it. The directory and its contents are entirely system-managed. The failure appears to happen inside neagent while it is handling the system-managed URL prefilter cache.

The failure occurs at the mmapToFile: step while neagent saves the Bloom filter prefilter data.

Directory state:

drwxr-xr-x  2  root  wheel  64  /private/var/db/urlPrefilter

Has anyone else encountered this? Any suggestions on what could cause neagent to fail with errno 13 on its own mmap file under /private/var/db/urlPrefilter?