[BUG] Claude Code Web default environment prevents fetching of github release artifacts

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When I start a Claude Code Web session in the default environment, it has trouble fetching release artifacts from GitHub. This is problematic because it prevents uv from installing required Python versions for projects that need a Python version that's not preinstalled in the default CCWeb environment.

uv says the following when trying to download a Python version:

error: Failed to install cpython-3.14.2-linux-x86_64-gnu
  Caused by: Request failed after 3 retries
  Caused by: Failed to download https://github.com/astral-sh/python-build-standalone/...
  Caused by: tunnel error: unsuccessful

while directing CC to fetch the url (https://github.com/astral-sh/python-build-standalone/releases/download/20260114/cpython-3.14.2%2B20260114-x86_64-unknown-linux-gnu-install_only_stripped.tar.gz) directly yields:

Exit code 56
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0HTTP/1.1 200 OK
date: Tue, 20 Jan 2026 14:51:34 GMT
server: envoy

HTTP/2 302 
date: Tue, 20 Jan 2026 14:51:16 GMT
content-type: text/html; charset=utf-8
content-length: 0
vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With,Accept-Encoding, Accept, X-Requested-With
location: https://release-assets.githubusercontent.com/github-production-release-asset/162334160/2db4a11b-0728-4a6f-83fc-a39e07cd29b8?sp=r&sv=2018-11-09&sr=b&spr=https&se=2026-01-20T15%3A25%3A59Z&rscd=attachment%3B+filename%3Dcpython-3.14.2%2B20260114-x86_64-unknown-linux-gnu-install_only_stripped.tar.gz&rsct=application%2Foctet-stream&skoid=96c2d410-5711-43a1-aedd-ab1947aa7ab0&sktid=398a6654-997b-47e9-b12b-9515b896b4de&skt=2026-01-20T14%3A25%3A29Z&ske=2026-01-20T15%3A25%3A59Z&sks=b&skv=2018-11-09&sig=b2EIqhKA87RKHeAl9u0f5kW8xlAl4SZoQeI7f9LxjEA%3D&jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJnaXRodWIuY29tIiwiYXVkIjoicmVsZWFzZS1hc3NldHMuZ2l0aHVidXNlcmNvbnRlbnQuY29tIiwia2V5Ijoia2V5MSIsImV4cCI6MTc2ODkyMjQ3NiwibmJmIjoxNzY4OTIwNjc2LCJwYXRoIjoicmVsZWFzZWFzc2V0cHJvZHVjdGlvbi5ibG9iLmNvcmUud2luZG93cy5uZXQifQ.5-2ElaIf-A0BHc8wYgj2MXDtKdzqD5coL_ByYnXZfEo&response-content-disposition=attachment%3B%20filename%3Dcpython-3.14.2%2B20260114-x86_64-unknown-linux-gnu-install_only_stripped.tar.gz&response-content-type=application%2Foctet-stream
cache-control: no-cache
######## A bunch of security headers omitted here ########
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (56) CONNECT tunnel failed, response 403

server: github.com
x-github-request-id: 1000:38A595:15C725:1F433F:696F9677

HTTP/1.1 403 Forbidden
x-deny-reason: host_not_allowed
content-length: 16
content-type: text/plain
date: Tue, 20 Jan 2026 14:51:34 GMT
server: envoy
connection: close

What Should Happen?

The default network profile should allow uv to download Python versions.

Error Messages/Logs

Steps to Reproduce

Create a new CCWeb session, asking Claude to:

Try to fetch https://github.com/astral-sh/python-build-standalone/releases/download/20260114/cpython-3.14.2%2B20260114-x86_64-unknown-linux-gnu-install_only_stripped.tar.gz

Or, alternatively, to:

Use uv to install Python 3.14 (`uv python install 3.14`)

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

N/A

Platform

Anthropic API

Operating System

Other

Terminal/Shell

Non-interactive/CI environment

Additional Information

_No response_