CVE-2021-3733
MEDIUMCVSS 6.5/10EPSS 4.67%
Last modified
CVE-2021-3733 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to, could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is sent by the server to the client. EPSS estimates a 4.67% chance of exploitation in the next 30 days.
Description
There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to, could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is sent by the server to the client. The greatest threat that this flaw poses is to application availability.
Metrics
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Python | Python | < 3.6.14 |
| Python | Python | >= 3.7.0, < 3.7.11 |
| Python | Python | >= 3.8.0, < 3.8.10 |
| Python | Python | >= 3.9.0, < 3.9.5 |
| Python | Python | 3.10.0 |
| Redhat | Codeready Linux Builder | 8.0 |
| Redhat | Codeready Linux Builder For Ibm Z Systems | 8.0 |
| Redhat | Codeready Linux Builder For Power Little Endian | 8.0 |
| Redhat | Enterprise Linux | 8.0 |
| Redhat | Enterprise Linux Eus | 8.4 |
| Redhat | Enterprise Linux For Ibm Z Systems | 8.0 |
| Redhat | Enterprise Linux For Ibm Z Systems Eus | 8.4 |
| Redhat | Enterprise Linux For Power Little Endian | 8.0 |
| Redhat | Enterprise Linux For Power Little Endian Eus | 8.4 |
| Redhat | Enterprise Linux Server Aus | 8.4 |
| Redhat | Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions | 8.4 |
| Redhat | Enterprise Linux Server Tus | 8.4 |
| Redhat | Enterprise Linux Server Update Services For Sap Solutions | 8.4 |
| Fedoraproject | Extra Packages For Enterprise Linux | 7.0 |
| Fedoraproject | Fedora | 33 |
| Fedoraproject | Fedora | 34 |
| Fedoraproject | Fedora | 35 |
| Fedoraproject | Fedora | 36 |
| Netapp | Management Services For Element Software And Netapp Hci | All versions |
| Netapp | Ontap Select Deploy Administration Utility | All versions |
| Netapp | Solidfire\, Enterprise Sds \& Hci Storage Node | All versions |
| Netapp | Hci Compute Node Firmware | All versions |
References
- https://bugs.python.org/issue43075Exploit, Issue Tracking, Patch, Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=1995234Issue Tracking, Third Party Advisory
- https://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fbPatch, Third Party Advisory
- https://github.com/python/cpython/pull/24391Patch, Third Party Advisory
- https://security.netapp.com/advisory/ntap-20220407-0001/Third Party Advisory
- https://ubuntu.com/security/CVE-2021-3733Patch, Third Party Advisory
- https://bugs.python.org/issue43075Exploit, Issue Tracking, Patch, Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=1995234Issue Tracking, Third Party Advisory
- https://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fbPatch, Third Party Advisory
- https://github.com/python/cpython/pull/24391Patch, Third Party Advisory
- https://security.netapp.com/advisory/ntap-20220407-0001/Third Party Advisory
- https://ubuntu.com/security/CVE-2021-3733Patch, Third Party Advisory
Timeline
- Published
- Last Modified
- Status
- Modified
Frequently Asked Questions
What is CVE-2021-3733?
There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to, could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is sent by the server to the client. The greatest threat that this flaw poses is to application availability.
How severe is CVE-2021-3733?
CVE-2021-3733 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 4.67% probability of exploitation in the next 30 days.
How do I fix CVE-2021-3733?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.
How Strix Helps
- How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
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Are you affected by CVE-2021-3733?
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