All external navigations hang at COMPUTED_PRIVACY_MODE / NETWORK_DELEGATE_BEFORE_START_TRANSACTION; localhost works (Linux Mint 22, BrowserOS v0.44.0.1)

[napter]

Summary

On Linux Mint 22 (Ubuntu 24.04), all external URL navigations hang at COMPUTED_PRIVACY_MODE / NETWORK_DELEGATE_BEFORE_START_TRANSACTION. Localhost works. Guest mode (--guest) works. Reproduces v0.39.0 through v0.44.0.1.

Root Cause (follow-up from Nathan Apter (@napter), 2026-05-07)

chrome/browser/enterprise/data_protection/data_protection_navigation_observer.cc:224 fires on every external navigation and triggers a RealTimeUrlLookupServiceBase::DoLookup async call that never completes its callback for non-guest profiles when CBCM is off and ESB is off.

Verbose log with --vmodule="*data_protection*=2" confirms:

enterprise.data_protection: URL to scan: https://example.com/

Request then stalls at COMPUTED_PRIVACY_MODE, never reaches NETWORK_DELEGATE_BEFORE_START_TRANSACTION.

Key isolation: --guest bypasses this code path entirely → pages load fine.

Things ruled out

• CBCM not enabled, ESB not set, no managed policy files on system
• --disable-features=SafeBrowsing,EnterpriseRealtimeURLChecks,RealTimeUrlLookup,DataProtectionUrlPing,SafeBrowsingHashPrefixRealTimeLookups — none help
• Brand-new --user-data-dir, --disable-extensions, --no-sandbox, --proxy-server=direct:// — none help
• Tailscale stopped, IPv6 disabled — no effect
• Managed policy JSON files with SafeBrowsingProtectionLevel: 0 — no effect
• Other Chromium browsers (Edge, Wavebox, system Chromium) work fine on same machine

Workaround

Launch with --guest (loses profile persistence).

Environment

• Linux Mint 22 / Ubuntu 24.04, kernel 6.8
• BrowserOS v0.44.0.1 (Chromium 146.0.7821.31), v0.43.0, v0.39.0.3

GitHub

#963

[napter]

Update — additional testing:

Version regression test (each with a fresh --user-data-dir, --disable-extensions):

• v0.44.0.1 (Chromium 146.0.7821.31) — hangs ❌
• v0.43.0 (Chromium 146.0.7818.31) — hangs ❌
• v0.39.0.3 (Chromium 142.0.7565.49) — hangs ❌

So this is not a recent regression — it reproduces back at least to v0.39.0 (Feb 2026), spanning three Chromium major versions.

Additional things ruled out:

• Stopped tailscaled (Tailscale was running on the machine) — same hang.
• AppArmor profile loaded but flagged unconfined (per the BrowserOS-shipped profile).
• /etc/<browser>/native-messaging-hosts/ and ~/.config/browser-os/NativeMessagingHosts/ are empty.

Since other Chromium-based browsers (Edge, Wavebox, system Chromium) work fine on this exact machine, this is something specific about how BrowserOS's chromium fork interacts with this Linux Mint 22 / Ubuntu 24.04 environment — but not a recent change. Happy to provide any further system info or test patches.

[napter]

Significant narrowing — --guest mode loads pages, regular mode doesn't

After much more diagnostic work I found two key data points that should make this very actionable:

1. --guest mode works, every regular-profile mode doesn't

/usr/bin/browseros --guest                                  → pages load ✅
/usr/bin/browseros --user-data-dir=/tmp/bos-clean           → hangs ❌
/usr/bin/browseros --user-data-dir=/tmp/bos-clean --disable-extensions  → hangs ❌

A brand-new --user-data-dir still hangs while --guest loads https://example.com, https://duckduckgo.com, etc. with full page render in <1 second.

So the bug is somewhere that differs between guest and regular profiles. Common chromium examples: enterprise data-protection navigation observer, real-time URL lookup service, sync, account consistency checks.

2. The verbose chromium log points at data_protection_navigation_observer.cc

With --enable-logging=stderr --vmodule="*data_protection*=2,*enterprise*=2", every navigation logs:

chrome/browser/enterprise/data_protection/data_protection_navigation_observer.cc:222]
enterprise.data_protection: same document navigation: 0
chrome/browser/enterprise/data_protection/data_protection_navigation_observer.cc:224]
enterprise.data_protection: URL to scan: https://example.com/

This fires for both internal (chrome://newtab/, chrome://policy/) and external URLs. Internal URLs subsequently load. External URLs hang at URL_REQUEST phase COMPUTED_PRIVACY_MODE and never advance to NETWORK_DELEGATE_BEFORE_START_TRANSACTION — exactly the phase where RealTimeUrlLookupServiceBase::DoLookup would be awaited.

CBCM is not enabled (log says Cloud management controller initialization aborted as CBCM is not enabled). Enhanced Safe Browsing is not set in fresh-profile preferences (safebrowsing.enhanced unset). No managed policy files exist on the system that affect this.

3. Other things that don't help

In addition to the previous list, none of these unstuck a regular profile:

• --disable-features=DnsOverHttps,DnsOverHttpsUpgrade
• IPv6 disabled system-wide via sysctl
• --disable-features=SafeBrowsing,SafeBrowsingHashPrefixRealTimeLookups,SafeBrowsingV5HashRealTimeOhttpQuery,EnterpriseRealtimeURLChecks,RealTimeUrlLookup,SafeBrowsingDeepScanning
• --disable-features=EnterpriseRealTimeUrlCheckMode,DataProtectionUrlPing,EnterpriseConnectorsAllowedSendingCookies plus a half-dozen other guesses
• Managed policy files at /etc/chromium/policies/managed/, /etc/browseros/policies/managed/, /etc/browser-os/policies/managed/ setting SafeBrowsingProtectionLevel: 0, all the On*EnterpriseConnector: [], etc.
• --safebrowsing-disable-auto-update, --disable-client-side-phishing-detection

So whatever the data-protection observer hands off to for non-guest profiles isn't gated by any of the standard flags or policies, but is bypassed in guest mode.

Workaround for users

Launch with --guest. Loses persistence but browser works.

Likely root cause area

In chrome/browser/enterprise/data_protection/data_protection_navigation_observer.cc (and the lookup service it calls into for non-guest, non-internal URLs), some async callback never fires on this Linux Mint 22 / Ubuntu 24.04 environment when CBCM is off, ESB is off, and no enterprise policy is set. Guest mode skips this code path entirely so it works.

Reproduces across:

• BrowserOS v0.44.0.1 (Chromium 146.0.7821.31)
• BrowserOS v0.43.0 (Chromium 146.0.7818.31)
• BrowserOS v0.39.0.3 (Chromium 142.0.7565.49)

I'm happy to provide additional logs, the netlog, or test patches.

[shadowfax92]

Hey Nathan Apter (@napter) — this is exceptional debugging work. You've narrowed it down to a specific Chromium code path (data_protection_navigation_observer.cc) with a clear guest-vs-regular-profile split and a concrete hypothesis about the async callback never firing for non-guest profiles when CBCM and ESB are both off.

A few things stand out:

• The --guest workaround is useful for users in the meantime
• The fact it reproduces across v0.39.0–v0.44.0.1 rules out a recent regression and points to something structural in how BrowserOS configures that code path for non-enterprise, non-guest profiles
• The RealTimeUrlLookupServiceBase::DoLookup stall at COMPUTED_PRIVACY_MODE is a very specific pinpoint

We're escalating this to engineering — this level of detail makes it very actionable. I'll add the bug label and flag it as high priority. Thank you for the thoroughness; reports like this save us significant investigation time.

[shadowfax92]

Nathan Apter (@napter) — following up on our acknowledgment above. Engineering has picked this up (tracked internally as TKT-798, priority: Urgent) and we want to move toward a targeted fix as quickly as possible. Two quick asks:

1. Patch testing
Engineering is preparing a build with the data-protection observer disabled for non-enterprise, non-guest profiles. Would you be willing to test that build when it's ready? It should be a straightforward drop-in replace of your current BrowserOS install. Your environment (Linux Mint 22 / Ubuntu 24.04, kernel 6.8) is exactly the reproduction case we need.

2. CBCM / ESB configuration confirmation
Your report mentions both are off — just want to confirm explicitly so engineering can document the exact reproducer state:

• CBCM (Chrome Browser Cloud Management): your system has never been enrolled in CBCM and chrome://policy shows no managed policies, correct?
• Enhanced Safe Browsing (ESB): safebrowsing.enhanced is unset (or false) in both fresh and existing profiles, correct?

In the meantime, the --guest flag remains the best workaround for day-to-day use. We'll keep this issue updated as engineering progresses. Apologies for the friction — this is clearly a real bug and your diagnostic work has made it very tractable to fix.

[shadowfax92]

[Triage — BrowserOS Engineering]

This is a confirmed known regression: data_protection_navigation_observer.cc stalls all external navigations at COMPUTED_PRIVACY_MODE for non-guest profiles when CBCM and ESB are both off. The async RealTimeUrlLookupServiceBase::DoLookup callback never fires in this configuration.

• Affects: Linux non-guest profiles, BrowserOS v0.39.0 – v0.44.0.1
• Does not affect: guest-mode profiles (--guest), Windows, macOS
• Root cause area: chrome/browser/enterprise/data_protection/data_protection_navigation_observer.cc — non-guest code path invokes a lookup service whose callback never resolves when no enterprise policy is active
• Workaround: launch with --guest (loses profile persistence)
• Internal tracking: TKT-798 (Urgent)
• Planned fix: data-protection observer guard for non-enterprise, non-guest profiles; patch build in preparation

[shadowfax92]

Hi Nathan Apter (@napter) — thanks for your detailed investigation and logs on this issue. Our engineering team has been digging into the hang at `COMPUTED_PRIVACY_MODE` and we have a strong lead on the root cause.

Hypothesis: Hash-Prefix Real-Time (HPRT) lookup stall

We've traced the hang to the Hash-Prefix Real-Time URL lookup service. On regular (non-guest) profiles, `DetermineHashRealTimeSelection` returns `kHashRealTimeService`, which creates an `AsyncCheckTracker` and fires background network requests to Google's HPRT servers. On Linux, if those requests stall (unreachable server, socket hang, or SQLite cookie store lock), the async callback never completes — and the navigation waits indefinitely. Guest profiles skip this path entirely, which is exactly why `--guest` works for you.

Layer 1 test — please try this

Could you relaunch BrowserOS with the following flag and confirm whether the hang disappears?

--disable-features=HashPrefixRealTimeLookups

Full launch example:

/path/to/browseros --disable-features=HashPrefixRealTimeLookups

Then try navigating to an external URL (e.g. https://example.com) on a non-guest profile and let us know:

• Does the hang disappear?
• Does navigation complete normally?

This will confirm (or rule out) HPRT as the Layer 1 cause. We're also working on a code-level fix (Layer 2 patch in `data_protection_navigation_observer.cc`) that we'll share with you once it's ready for testing.

Thank you!

[napter]

Thanks for picking this up so quickly — happy to keep testing.

Layer 1 test: --disable-features=HashPrefixRealTimeLookups

Result: hang persists. HPRT disable does not unstick external navigations on a non-guest profile.

Test setup:

• BrowserOS v0.44.0.1 (current install, Chromium 146.0.7821.31)
• Fresh --user-data-dir=/tmp/bos-hprt, --disable-extensions
• Flag confirmed applied in running args: --disable-features=HashPrefixRealTimeLookups

Navigated four URLs via /json/new (CDP):

• https://example.com/ → hangs (title empty after 25s+)
• https://duckduckgo.com/ → hangs
• https://wikipedia.org/ → hangs
• http://1.1.1.1/ → hangs

All four show the same pattern as before: URL committed, content never loads, title stays empty (or shows the prior tab's "New Tab" title). --guest mode on this same install still loads pages instantly, so the regression-vs-guest split is unchanged.

If it's useful, related-name variants I'd already tried earlier in this thread (also did not help):

• --disable-features=SafeBrowsingHashPrefixRealTimeLookups
• --disable-features=SafeBrowsingV5HashRealTimeOhttpQuery
• --disable-features=SafeBrowsing (the umbrella)

CBCM / ESB confirmation (your ask #2)

CBCM: Confirmed never enrolled. chrome://policy on a freshly launched profile shows policies_count: 0, no enrollment token, and the "no policies set" hint message. Earlier verbose-log run also showed Cloud management controller initialization aborted as CBCM is not enabled at startup.

ESB: Confirmed off. In both the fresh test profile and my existing ~/.config/browser-os/Default/Preferences, the safebrowsing block looks like:

{
  "event_timestamps": {},
  "metrics_last_log_time": "...",
  "scout_reporting_enabled_when_deprecated": false
}

Neither safebrowsing.enhanced nor safebrowsing.enabled is set, so both fall back to Chromium defaults (Standard SB on, Enhanced SB off).

Ready for the Layer 2 patch build whenever it's ready

Linux Mint 22 (Ubuntu 24.04 base, kernel 6.8) — exact repro environment. Just point me at the build and I'll test the same matrix (example.com / duckduckgo.com / 1.1.1.1, fresh and existing profile, with and without --guest) and report back same-day if possible.

Happy to gather any additional data in the meantime — strace of the network process during a hung nav, a longer netlog, or chrome://histograms snapshots before/after a nav. Let me know.