CVE-2021-39214: Lacking Protection against HTTP Request Smuggling in mitmproxy
Impact
In mitmproxy 7.0.2 and below, a malicious client or server is able to perform HTTP request smuggling attacks through mitmproxy. This means that a malicious client/server could smuggle a request/response through mitmproxy as part of another request/response's HTTP message body. While mitmproxy would only see one request, the target server would see multiple requests. A smuggled request is still captured as part of another request's body, but it does not appear in the request list and does not go through the usual mitmproxy event hooks, where users may have implemented custom access control checks or input sanitization.
Unless you use mitmproxy to protect an HTTP/1 service, no action is required.
Patches
The vulnerability has been fixed in mitmproxy 7.0.3 and above.
Acknowledgements
We thank João Sobral (@chinchila) for responsibly disclosing this vulnerability to the mitmproxy team.
Timeline
- 2021-09-08: Received initial report for mitmproxy <= 6.0.2. - 2021-09-08: Requested clarification if 7.x is affected. - 2021-09-10: Received additional details, 7.x situation still unclear. - 2021-09-13: Internally determined that 7.x is also affected. - 2021-09-13: Shared initial fix with researcher. - 2021-09-14: Received confirmation that fix is working, but H2.TE/H2.CL should also be looked at. - 2021-09-14: Shared revised fix that includes additional H2.TE mitigations. - 2021-09-14: Received confirmation that revised fix is working. - 2021-09-16: Completed internal patch review. - 2021-09-16: Published patch release and advisory.
Other sources
mitmproxy is an interactive, SSL/TLS-capable intercepting proxy. In mitmproxy 7.0.2 and below, a malicious client or server is able to perform HTTP request smuggling attacks through mitmproxy. This means that a malicious client/server could smuggle a request/response through mitmproxy as part of another request/response's HTTP message body. While a smuggled request is still captured as part of another request's body, it does not appear in the request list and does not go through the usual mitmproxy event hooks, where users may have implemented custom access control checks or input sanitization. Unless one uses mitmproxy to protect an HTTP/1 service, no action is required. The vulnerability has been fixed in mitmproxy 7.0.3 and above.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/mitmproxyto a version that resolves this vulnerability.Fixed in 7.0.3 - Upgrade
Upgrade
mitmproxyto a version that resolves this vulnerability.Fixed in 7.0.3 - Compensating control
If you use mitmproxy to protect an HTTP/1 service, mitigate by upgrading mitmproxy to a version where HTTP request smuggling is fixed (mitmproxy 7.0.3 and above). If you do not use mitmproxy to protect an HTTP/1 service, no action is required per the advisory.
Event History
Frequently Asked Questions
What is the severity of CVE-2021-39214?
CVE-2021-39214 has a medium severity rating due to the potential for HTTP request smuggling attacks.
How do I fix CVE-2021-39214?
To fix CVE-2021-39214, upgrade mitmproxy to version 7.0.3 or higher.
Which versions of mitmproxy are affected by CVE-2021-39214?
CVE-2021-39214 affects mitmproxy versions 7.0.2 and below.
What type of attack is associated with CVE-2021-39214?
CVE-2021-39214 is associated with HTTP request smuggling attacks.
Can a malicious client exploit CVE-2021-39214?
Yes, a malicious client can exploit CVE-2021-39214 to perform HTTP request smuggling.