cca-engine fetch() bypasses HTTPS_PROXY on self-hosted runners with restricted egress

[GaryB477]

🏷️ Discussion Type

Bug

💬 Feature/Topic Area

Copilot Cloud Agent

Body

Problem

Note

If you believe this to not be the correct place for this inquiry, feel free to let me know! I did not find any real related GH repositories where I could open an issue for this :)

We run Copilot coding agents on ARC-managed self-hosted runners with hardened egress (Squid sidecar + iptables default-DENY). The runner container has HTTPS_PROXY=http://127.0.0.1:3128 configured. However, the runner does NOT seem to respect HTTPS_PROXY or similar settings.

As a result, the agent makes direct TCP connections to GitHub IPs and fails closed with:

[cca-engine] Fatal: TypeError: fetch failed

eBPF trace shows the direct connect:

12:39:19 comm=MainThread -> 140.82.114.21:443

--> This problem was first discovered starting May 27. 2026. Prior, it worked without any problems.

Reproduction

ARC runner with iptables OUTPUT policy DROP, only loopback + UID-13 (squid) on 80/443 permitted. cca-engine job fails on fetch().

Workaround we ended up with

Allowlist GitHub published /20+/22 CIDRs at the iptables level for TCP/443 from any UID:

• 140.82.112.0/20
• 143.55.64.0/20
• 192.30.252.0/22

This breaks the Squid hostname-allowlist guarantee for traffic that lands on those CIDRs, which is roughly equivalent risk to the existing .github.com Squid wildcard.

Asks

1. Were there any changes regarding this? I would suspect that this is a node
   related problem ([upstream Support HTTP_PROXY and NO_PROXY env var nodejs/undici#1650], [Node PR localhost not working #57165]).
2. If that's not the case, can someone publish the minimum set of hosts/IPs that
   cca-engine connects to, separate from the existing cloud-agent
   allowlist?
   Current docs explicitly state "firewall is not compatible
   with self-hosted runners" — that pushes orgs with strict egress
   policy into a hard choice between "disable firewall entirely" and
   "reverse-engineer the agent's traffic."

Related issues:

• Support HTTP_PROXY and NO_PROXY env var nodejs/undici#1650 (proxy env var support, root cause)
• GitHub Copilot CLI fails with "fetch failed" error in corporate environments with SSL inspection github/copilot-cli#333 (similar fetch-failed pattern with proxies)

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