[Bug]: macOS client modifies another app's keychain item on startup (sets partition list to teamid:NKUJUXUJ3B), breaking Claude Code #10976

⚠️ Before submitting, please verify the following: ⚠️

• This is a bug, not a question or a configuration issue.
• This issue is not already reported on Github (I have searched for it).
• Nextcloud Server and Desktop Client are up to date. See Server Maintenance and Release Schedule and Desktop Releases for supported versions.
• I agree to follow Nextcloud's Code of Conduct

Bug description

On every startup, the Nextcloud desktop client modifies a keychain item that does not belong to it: the generic password Claude Code-credentials (account = my macOS username), created by Claude Code (Anthropic's CLI).

After Nextcloud starts, that item's partition list becomes teamid:NKUJUXUJ3B (Nextcloud's team ID, confirmed with codesign -dv /Applications/Nextcloud.app) instead of apple-tool:. From then on, every other app that reads the item, including /usr/bin/security (which Claude Code uses), is blocked by the partition-list check. macOS shows a "security wants to access key 'Claude Code-credentials'" dialog that can't be dismissed: Allow, Always Allow and Deny all just make it come back.

Evidence

I ran a watcher that logged the item's partition_id and modification date every 5–15 s across a reboot:

No Claude process was running when the item was modified, and no other keychain items were affected. My guess is that a keychain update/write query matches on the account name only (the macOS username, which equals my Nextcloud username) and not on the service, so it hits the first generic password with that account.

Other Claude Code users with Nextcloud installed report the same symptom:

• [BUG] macOS: Claude Code locks itself out of its own keychain credential → endless "security wants to access Claude Code-credentials" password prompts anthropics/claude-code#81707
• macOS: Keychain item written without trusted-application list -> auth prompt on every credential read anthropics/claude-code#77697

Steps to reproduce

1. On macOS, have a generic keychain password created by another tool whose account equals your macOS username (in my case the same as the Nextcloud username), e.g. log in to Claude Code, or:
   security add-generic-password -s "Test-item" -a "$USER" -w x
2. Check its partition_id (should be apple-tool:):
   security dump-keychain -a ~/Library/Keychains/login.keychain-db | grep -A20 '"svce"<blob>="Test-item"' | grep -A2 partition_id
3. Reboot (Nextcloud starts at login).
4. The item's partition_id is now teamid:NKUJUXUJ3B, and reading it with /usr/bin/security triggers a keychain password dialog.

(Observed with the Claude Code item across several reboots; the generic test item in step 1 is my suggested minimal repro.)

Expected behavior

Nextcloud should only read and write its own keychain items (match on service and account), and never change the access control / partition list of other apps' items.

Which files are affected by this bug

None (not a file sync issue; affects macOS login keychain item "Claude Code-credentials")

Operating system

macOS

Which version of the operating system you are running.

macOS 27.0.1

Installation method

Official Installer for macOS 13 and later

Nextcloud Server version

34.0.4

Nextcloud Desktop Client version

34.0.4

Did this occur after an update or on a clean installation?

Minor version update (i.e. 33.0.0 → 33.0.1)

Are you using the Nextcloud Server Encryption module?

No

Are you using an external user-backend?

• Default internal user-backend
• LDAP or Active Directory
• SSO - SAML
• Other

Nextcloud Server logs

Additional info

Workaround (has to be repeated after every Nextcloud start):

security set-generic-password-partition-list -S apple-tool:,apple:,teamid:NKUJUXUJ3B -s "Claude Code-credentials" -a "$USER"

Command used to check the partition list:

security dump-keychain -a ~/Library/Keychains/login.keychain-db | awk '/"svce"<blob>="Claude Code-credentials"/{f=1} f&&/partition_id/{getline; getline; print; exit}'

Claude Code version: 2.1.286