mcp: add tools/call request transcocding. by guoyilin42 · Pull Request #43742 · envoyproxy/envoy

guoyilin42 · 2026-03-03T20:52:53Z

Commit Message: mcp: add tools/call request transcocding.
Additional Description: N/A
Risk Level: Low
Testing: Unit test
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional API Considerations:]

Signed-off-by: Yilin Guo <guoyilin@google.com>

guoyilin42 · 2026-03-03T20:55:06Z

@paulhong01

yanavlasov · 2026-03-04T17:45:38Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces support for tools/call request transcoding in the MCP JSON REST bridge. However, it introduces a high-severity path traversal vulnerability in the URL construction logic due to permissive percent encoding in path templates, potentially allowing attackers to inject path traversal sequences. Additionally, there is a medium-severity risk of sensitive data exposure because the full request body is logged at the info level, which may leak sensitive tool arguments. The core logic is in http_request_builder.cc and has unit tests. Please address these security concerns to ensure the safety and integrity of the system.

source/extensions/filters/http/mcp_json_rest_bridge/http_request_builder.cc

source/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter.cc

source/extensions/filters/http/mcp_json_rest_bridge/http_request_builder.cc

Signed-off-by: Yilin Guo <guoyilin@google.com>

tyxia · 2026-03-05T01:47:17Z

/gemini review

agrawroh · 2026-03-05T02:05:05Z

@tyxia I think the Gemini Review stopped working for some reason :(

botengyao · 2026-03-05T02:06:32Z

It was disabled intentionally to figure out the trigger per @yanavlasov

tyxia · 2026-03-05T02:12:44Z

@agrawroh @botengyao , yeah it is probably disabled in #43772

I hope it still can be invoked manually by command like /gemini review / or auto-enabled on the PR that is ready for review.

paulhong01

Thanks!

source/extensions/filters/http/mcp_json_rest_bridge/http_request_builder.cc

Signed-off-by: Yilin Guo <guoyilin@google.com>

agrawroh · 2026-03-06T19:42:11Z

/gemini review

gemini-code-assist

Code Review

This pull request adds support for tools/call request transcoding in the MCP JSON REST bridge filter, introducing a new HttpRequestBuilder for constructing HTTP requests from JSON-RPC tool calls. However, a high-severity Path Traversal / URL Manipulation vulnerability has been identified in http_request_builder.cc. The constructBaseUrl function fails to URL-encode values from the untrusted arguments JSON object before inserting them into the URL path template, which could allow an attacker to manipulate the resulting URL and access unintended backend endpoints. While the overall implementation is well-organized and thoroughly tested, there is also a suggestion to enhance the readability and performance of JSON parsing within the filter.

source/extensions/filters/http/mcp_json_rest_bridge/http_request_builder.cc

source/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter.cc

Signed-off-by: Yilin Guo <guoyilin@google.com>

botengyao

Nice, thanks for moving this forward! lgtm module some questions.

/wait

source/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter.cc

source/extensions/filters/http/mcp_json_rest_bridge/http_request_builder.cc

source/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter.cc

source/extensions/filters/http/mcp_json_rest_bridge/http_request_builder.cc

test/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter_test.cc

tyxia

Thanks for your contribution!

As buffering issue i pointed out below, please add the integration test to verify that this PR is working end to end.

source/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter.cc

click wrong approval here.

Signed-off-by: Yilin Guo <guoyilin@google.com>

agrawroh

Looks good to me. I'll wait for @botengyao to do a final pass.

agrawroh

I had an offline discussion with @tyxia and re-reviewed some of the parts which I didn't pay close attention to. This feedback from @tyxia is a MUST-fix before we should ship it. Please address the gaps.

Signed-off-by: Yilin Guo <guoyilin@google.com>

tyxia

Thanks for contribution! LGTM as a baseline implementation.

Please add buffer protection in the next PR to ensure this filter is production ready,

test/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_integration_test.cc

source/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter.cc

tools/spelling/spelling_dictionary.txt

botengyao

@guoyilin42 could also merge main?

Signed-off-by: Yilin Guo <guoyilin@google.com>

guoyilin42 · 2026-03-12T17:57:50Z

@guoyilin42 could also merge main?

Done.

botengyao · 2026-03-12T19:04:09Z

/retest

agrawroh

LGTM, Thanks!

Commit Message: mcp: add tools/call request transcocding. Additional Description: N/A Risk Level: Low Testing: Unit test Docs Changes: N/A Release Notes: N/A Platform Specific Features: N/A [Optional Runtime guard:] [Optional Fixes #Issue] [Optional Fixes commit #PR or SHA] [Optional Deprecated:] [Optional [API Considerations](https://github.com/envoyproxy/envoy/blob/main/api/review_checklist.md):] --------- Signed-off-by: Yilin Guo <guoyilin@google.com> Signed-off-by: bjmask <11672696+bjmask@users.noreply.github.com>

Commit Message: mcp: add tools/call request transcocding. Additional Description: N/A Risk Level: Low Testing: Unit test Docs Changes: N/A Release Notes: N/A Platform Specific Features: N/A [Optional Runtime guard:] [Optional Fixes #Issue] [Optional Fixes commit #PR or SHA] [Optional Deprecated:] [Optional [API Considerations](https://github.com/envoyproxy/envoy/blob/main/api/review_checklist.md):] --------- Signed-off-by: Yilin Guo <guoyilin@google.com>

mcp: add tools/call request transcocding.

a68bd16

Signed-off-by: Yilin Guo <guoyilin@google.com>

guoyilin42 requested review from botengyao, tyxia and yanavlasov as code owners March 3, 2026 20:52

gemini-code-assist bot reviewed Mar 4, 2026

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ggreenway assigned yanavlasov Mar 4, 2026

guoyilin42 added 2 commits March 4, 2026 19:26

Address comments.

e11213e

Signed-off-by: Yilin Guo <guoyilin@google.com>

Merge remote-tracking branch 'origin/main' into mcp

7c03e96

Signed-off-by: Yilin Guo <guoyilin@google.com>

tyxia assigned botengyao, tyxia and paulhong01 Mar 5, 2026

paulhong01 approved these changes Mar 5, 2026

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source/extensions/filters/http/mcp_json_rest_bridge/http_request_builder.cc Show resolved Hide resolved

Address comments.

42eed32

Signed-off-by: Yilin Guo <guoyilin@google.com>

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source/extensions/filters/http/mcp_json_rest_bridge/http_request_builder.cc Outdated Show resolved Hide resolved

source/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter.cc Outdated Show resolved Hide resolved

Address gemini review comments.

f1c02c8

Signed-off-by: Yilin Guo <guoyilin@google.com>

botengyao previously approved these changes Mar 9, 2026

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repokitteh-read-only bot added the waiting label Mar 9, 2026

tyxia reviewed Mar 9, 2026

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source/extensions/filters/http/mcp_json_rest_bridge/mcp_json_rest_bridge_filter.cc Outdated Show resolved Hide resolved

guoyilin42 added 2 commits March 9, 2026 23:35

Address comments.

1008526

Signed-off-by: Yilin Guo <guoyilin@google.com>

Fix format.

46eb64b

Signed-off-by: Yilin Guo <guoyilin@google.com>

repokitteh-read-only bot removed the waiting label Mar 9, 2026

Merge remote-tracking branch 'origin/main' into mcp

81fe714

Signed-off-by: Yilin Guo <guoyilin@google.com>

Fix spelling.

925d267

Signed-off-by: Yilin Guo <guoyilin@google.com>

agrawroh approved these changes Mar 10, 2026

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agrawroh requested changes Mar 10, 2026

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guoyilin42 added 2 commits March 10, 2026 19:42

Fix format.

248d8e6

Signed-off-by: Yilin Guo <guoyilin@google.com>

Merge remote-tracking branch 'origin/main' into mcp

a24a1c1

Signed-off-by: Yilin Guo <guoyilin@google.com>

tyxia previously approved these changes Mar 12, 2026

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botengyao previously approved these changes Mar 12, 2026

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guoyilin42 added 2 commits March 12, 2026 17:53

Address comments.

fb33286

Signed-off-by: Yilin Guo <guoyilin@google.com>

Merge remote-tracking branch 'origin/main' into mcp

4afd7fb

Signed-off-by: Yilin Guo <guoyilin@google.com>

guoyilin42 dismissed stale reviews from botengyao and tyxia via 4afd7fb March 12, 2026 18:03

tyxia approved these changes Mar 12, 2026

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guoyilin42 requested a review from agrawroh March 12, 2026 18:39

agrawroh approved these changes Mar 12, 2026

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botengyao merged commit 43e718e into envoyproxy:main Mar 12, 2026
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guoyilin42 deleted the mcp branch March 16, 2026 18:38

guoyilin42 mentioned this pull request Mar 27, 2026

MCP: mcp_json_rest_bridge filter progress #44146

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