alkhttp/tasks/adapters/review-002-fwd13-dot-segments.md

id, name, status, depends_on, scope, risk, impact, level, tags

id	name	status	depends_on	scope	risk	impact	level	tags
review-002-fwd13-dot-segments	Reject lone dot-dot path values that Url-set_path normalizes away (FWD-13)	completed		narrow	medium	component	implementation	adapters review-002 security from-openapi

Description

Review 002 FWD-13 [major, security]. Lone ./.. path-parameter values survive the PATH_VALUE_ENCODE_SET (which has no .) and are silently normalized away by Url::set_path — empirically reproduced against the locked url 2.5.8:

• set_path("/tenants/../admin") → /admin
• set_path("/files/..") → /
• set_path("/repos/%2e%2e/x") → /x (so adding %2e to the encode set would NOT fix it — the parser normalizes every case-insensitive spelling)

Scenario: template /tenants/{tenant}/resources with peer input tenant = ".." → the upstream receives /resources — a different (east commonly less-scoped, list-everything) endpoint than the template describes, with the namespace's injected credentials attached. The existing dot-segment test (traversal_value_cannot_escape_template_path, forward.rs:1155) only covers the multi-segment ../../admin form the encoder does catch. The origin check in assemble_request_url (:520-522) cannot catch this — the origin never changes.

Acceptance Criteria

• Rendered path values that are exactly . or .. (case-insensitive, including %2e spellings before encoding) are rejected with a loud INVALID_INPUT-family CallError — the cleanest point is value_to_path_segment / render_path_template
• A post-set_path invariant assert (decoded path segments = base_dir + rendered segments, byte-identical) protects against future normalizer surprises (implementer's choice: debug_assert + loud runtime check, or a property test with a dot/percent/binary corpus)
• Tests: lone .. value → error; lone . value → error; %2e%2e spelling → error; a legitimate segment containing a dot (v1.2.3, .hidden-file as a value) still works (the rejection is exact-match, not substring)
• Existing traversal/encoding tests unchanged and passing
• cargo test, cargo clippy --all-targets -- -D warnings, cargo fmt --check pass

References

• docs/reviews/002-post-remediation-review.md (Part D', FWD-13)
• src/adapters/forward.rs:340-352 (encode set lacking .), :413-448 (renderer), :481-531 (set_path + origin check), :1155 (the test family)
• tasks/adapters/review-001-forward-url-safety.md (the FWD-01 fix this completes — one case short)

Notes

The error message must not echo the raw value's neighbor inputs (no spec/content leakage beyond the parameter name — follow the existing message style in render_path_template's unbound-placeholder error). FWD-18 (object/array placeholder values double-routing to query) is tracked separately in review-002-fwd17-19-contract-decisions — do not fold it here, the mechanisms are adjacent but the decisions differ.

Summary

Lone ./.. (and %2e spellings) path values rejected INVALID_INPUT at value_to_path_segment; post-set_path normalization invariant in assemble_request_url; url 2.5.8 normalization empirically pinned; dotted-value legitimacy + segment-survival corpus tests.