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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

← All of v2.1.251 Home All releases ←olderv2.1.250
Claude Code v2.1.251

Custom headers from settings are now validated before reaching the environment

You'll notice
Useful3 Signal3
Settings

Custom headers from settings are validated before entering the environment.

ANTHROPIC_CUSTOM_HEADERS
What

A ANTHROPIC_CUSTOM_HEADERS value supplied through settings used to be copied into the process environment unchecked. It now has to pass a validation step first, closing a path where settings could inject arbitrary header material.

Details
  • Rejects bare carriage-return line endings and any header line whose value looks like a redirect payload.
  • Rejects header names matching a broad sensitive-key pattern covering auth, key, token, cookie, secret, credential, session, signature, passw and jwt.
  • Always enforced; this removes a previous bypass rather than adding an opt-in.
Evidence

ANTHROPIC_CUSTOM_HEADERS

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.251 →