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Author: Howard Enos
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Timestamp: 2026-06-08 15:25:56
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# Cascades of Tucson — Session Log 2026-06-08 — Edge UNC Download Bug Diagnosis
## User
- **User:** Howard Enos (howard)
- **Machine:** Howard-Home
- **Role:** tech
## Session Summary
Diagnosed (no changes made) a user-reported issue at Cascades: Ashley Jensen
(DESKTOP-U2DHAP0, domain-joined, Downloads folder redirected to the `\\cs-server\homes`
UNC share) could not open Office downloads from the Microsoft Edge download list. Clicking
a downloaded `.xlsx`/`.docx` in Edge produced "Windows cannot find
'\\?\\\cs-server\homes\AshleyJensen\Downloads\<file>'." Text files and PDFs opened fine
from the same Edge action; the same Office files opened fine when double-clicked from File
Explorer. Howard wanted root cause first, not a fix.
Worked the symptom to a root cause: the `\\?\` is the Win32 extended-length path prefix, and
the error path is the malformed result of prepending `\\?\` to a UNC path (`\\?\` + `\\cs-server`
= `\\?\\\cs-server`) instead of the correct `\\?\UNC\cs-server\...`. Confirmed with Howard's
test that Explorer double-click works and only the Edge download-list "open" fails — isolating
the fault to Edge's open-from-download invocation, not the file, share, or folder redirection.
Howard found and supplied the canonical upstream bug: Chromium issue 519243472, "Can't open
downloaded file when Downloads folder is a UNC path (malformed `\\?\` path on open)" — Status
Fixed, P0/S2, component UI>Browser>Downloads. The report confirms the exact mechanism: a
**regression introduced in Chromium 149** (last good 148.0.7778.217, first bad 149.0.7827.54)
in the `LaunchShellExecuteViaExplorer` feature, which prepends `\\?\` to a UNC path without
converting to `\\?\UNC\`. Triggered specifically by Downloads redirected via Folder Redirection
to a network UNC path with no mapped drive — exactly Ashley's configuration. The earlier
"Open Office files in the browser" theory was retracted; that was not the cause.
Confirmed applicability to Cascades: Ashley and Lois Lane are on **Edge 149.0.4022.52** (June 4,
2026 stable). Edge rides the Chromium 149 base, so it inherits the regression (the original
reporter thought Edge was immune, but bug comment #27, dated 2026-06-08, confirms Edge affected
in RDS/Citrix/AVD). The txt/pdf-work-Office-fails split is explained by only the external
ShellExecute launch path being broken (PDF opens in Edge's built-in viewer; Office routes
through the broken launch). Presented fix options ranked for the HIPAA environment: update Edge
forward into the fix, the `--disable-features=LaunchShellExecuteViaExplorer` flag, "Show in
folder" workaround, or a supported 149→148 MSI rollback. Howard asked about a simple
"uninstall the update" rollback; clarified Edge is not serviced via Windows Update so no
per-update revert exists — the MSI + `RollbackToTargetVersion` + version-pin is the only
supported downgrade. No changes were applied this session; decision on fix path left to Howard.
## Key Decisions
- Diagnosed root cause before proposing any fix, per Howard's explicit "no changes, figure out
the cause" instruction. Treated the Explorer-works / Edge-fails split as the key discriminator.
- Retracted the intermediate "Open Office files in the browser" hypothesis once the Chromium bug
report identified `LaunchShellExecuteViaExplorer` as the actual regression. Did not defend the
earlier guess.
- Recommended the lighter fixes (feature flag, wait for the fixed Edge 149.x, or "Show in folder")
over a full version rollback for HIPAA machines, because pinning to 148 forfeits 149 security
fixes and must be unwound later. Provided the full supported rollback procedure anyway since
Howard requested it.
- Flagged the issue as fleet-wide, not Ashley-specific: every Cascades user with Downloads
redirected to the `\\cs-server\homes` UNC share will hit it once on Edge 149 (the whole
domain-migrated set plus the caregiver/medtech machines using the same redirect pattern).
## Problems Encountered
- Could not fetch the Reddit thread or the Chromium tracker pages directly — Reddit is hard-blocked
for WebFetch, and `issues.chromium.org` / `issuetracker.google.com` are JS apps behind sign-in
that return only the login shell. Web search did not surface the specific issue. Resolved when
Howard copy-pasted the full bug report text, which provided the authoritative root cause,
regression range, and fix status.
## Configuration Changes
- None. Diagnostic-only session. No tenant, RMM, GPO, or repo config changed.
- This session log created: `clients/cascades-tucson/session-logs/2026-06/2026-06-08-howard-edge-unc-download-bug-diagnosis.md`.
## Credentials & Secrets
- None discovered or created this session. (Separately this day, the Lonestar Electrical Unraid
root password was read from the vault on request — entry `clients/lonestar/unraid-server.sops.yaml`;
not a Cascades item, value not reproduced here.)
## Infrastructure & Servers
- **Affected machines:** DESKTOP-U2DHAP0 (Ashley Jensen), DESKTOP-KQSL232 (Lois Lane) — both on Edge 149.0.4022.52.
- **Redirect target:** `\\cs-server\homes\<user>\Downloads` (CS-SERVER 192.168.2.254, file server / homes share `D:\Homes`). No mapped drive — raw UNC, which is the bug's required trigger.
- **Edge stable app GUID (for EdgeUpdate pin):** `{56EB18F8-B008-4CBD-B6D2-8C97FE7E9062}`.
## Commands & Outputs
- Error dialog (verbatim from screenshot): `Windows cannot find '\\?\\cs-server\homes\AshleyJensen\Downloads\Resident Demographics Table.xlsx'. Make sure you typed the name correctly, and then try again.`
- Discriminator test (Howard): double-click the same xlsx from File Explorer at `\\cs-server\homes\AshleyJensen\Downloads` → opens normally. Only the Edge download-list "open" fails.
- Edge version check (Howard): Ashley + Lois both `149.0.4022.52`.
### Fix options (reference — none applied)
1. **Update Edge forward** into the fixed build (permanent; Chromium fix crrev 7900033 "Correctly handle UNC paths in InvokeShellExecute", merged M149/M150, verified Chromium 151.0.7875.0). Re-enabled the feature after fixing, so the code fix — not a disabled flag — is the real resolution.
2. **Feature flag (interim):** Edge shortcut target →
`"C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe" --disable-features=LaunchShellExecuteViaExplorer`
(fully quit Edge first; only applies to launches from that shortcut).
3. **"Show in folder"** in the Edge download list → open from Explorer (zero-config; confirmed working).
4. **Supported 149→148 rollback** (one major back is in-bounds):
- Download 148 stable **MSI** from https://www.microsoft.com/en-us/edge/business/download (Stable / 148 / Win x64).
- `HKLM\SOFTWARE\Policies\Microsoft\Edge` → `RollbackToTargetVersion` (DWORD) = 1 *(set BEFORE install; enables downgrade + preserves profile).*
- `HKLM\SOFTWARE\Policies\Microsoft\EdgeUpdate` → `TargetVersionPrefix{56EB18F8-B008-4CBD-B6D2-8C97FE7E9062}` (REG_SZ) = `148.` and `Update{56EB18F8-...}` (DWORD) = 2 (manual) *(pins it; else auto-update returns to 149).*
- Install 148 MSI → verify `edge://version` = 148.x and `edge://policy` shows the rollback + target-prefix active.
- Unwind later (`RollbackToTargetVersion=0`, remove `TargetVersionPrefix`) once a fixed Edge 149.x/150 ships.
## Pending / Incomplete Tasks
- **Decision pending (Howard):** pick fix path for Ashley + Lois — feature flag vs "Show in folder" vs 148 MSI rollback vs wait for fixed Edge 149.x. No changes made this session.
- **Fleet exposure:** all Cascades users with Downloads redirected to `\\cs-server\homes` + Edge 149 will hit this (Sharon Edwards, Crystal Rodriguez, Lauren Hasselman, Megan Hiatt, receptionist/nursestation, and the caregiver/medtech machines). Decide whether to fix fleet-wide (lean flag/wait, not a fleet-wide 148 pin, to avoid holding the fleet off security updates).
- **Offered, not yet run:** read-only RMM pull of Edge version + update channel across the Cascades agent fleet to quantify how many machines are on the affected 149 build.
- **Watch:** Edge stable release notes for the servicing build that carries the InvokeShellExecute UNC fix; flag it so pinned/rolled-back machines can go forward.
- Unrelated and still open from prior session: caregiver/medtech Monday go-live runbook (reboot/verify NURSESTATION lockdown, ALIS timeout 20→15, CA allow-list + GPO filter cutover, laptop hybrid-join gap).
## Reference Information
- **Chromium issue 519243472** — "Can't open downloaded file when Downloads folder is a UNC path (malformed `\\?\` path on open)". Status Fixed, P0/S2, UI>Browser>Downloads. Regression Chromium 149 (last good 148.0.7778.217, first bad 149.0.7827.54). Feature: `LaunchShellExecuteViaExplorer`. Fix: crrev 7900033, merged M149/M150, verified 151.0.7875.0. Related save-side bug: 40888395.
- Edge stable 149.0.4022.52 release notes: https://learn.microsoft.com/en-us/deployedge/microsoft-edge-relnote-stable-channel#version-1490402252-june-04-2026-stable
- Edge for Business download (MSI): https://www.microsoft.com/en-us/edge/business/download
- Chrome interim mitigation history (from bug): Finch/variations config disabling the feature pushed 2026-06-04 (no reboot if variations enabled); Edge delivers its own equivalent via `config.edge.skype.com`.
- Source Reddit thread (could not fetch; Howard-supplied): https://www.reddit.com/r/sysadmin/comments/1txi9ur/edge_downloads_location_with_unc_path/
- Cascades wiki: `wiki/clients/cascades-tucson.md`. Ashley Jensen recorded there as DESKTOP-U2DHAP0 (domain-joined, folder redirect manually fixed); Lois Lane as DESKTOP-KQSL232 (CareTakers dept head).