# CVE-2021-3733: Denial of service in python > A malicious HTTP server can cause a Regular Expression Denial of Service in Python's urllib authentication handler, impacting application availability. - **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 7 Mar 2022 - **Updated:** 14 Oct 2026 - **Also known as:** AZL-109638, BIT-libpython-2021-3733, BIT-python-2021-3733, BIT-python-min-2021-3733, CLSA-2024-1722527236, CLSA-2024-1723146030, DEBIAN-CVE-2021-3733, GHSA-wj55-vqcq-gxcp, MGASA-2021-0457, PSF-2022-6, RHSA-2021:4057, UBUNTU-CVE-2021-3733 ## What is CVE-2021-3733? CVE-2021-3733 is a medium-severity denial of service vulnerability in Fedoraproject Extra Packages for Enterprise Linux, published on 7 Mar 2022. Any signed-in user can exploit it over the network, with no action from the victim. ### Official 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. Weakness: CWE-400 (Uncontrolled Resource Consumption) ## Which versions are affected by CVE-2021-3733? 3 open source packages ship an affected version, including libpython, python and python-min. It affects 20 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `libpython` | Bitnami | All versions | 3.6.14, 3.7.11, 3.8.10, 3.9.5 | | `python` | Bitnami | All versions | 3.6.14, 3.7.11, 3.8.10, 3.9.5 | | `python-min` | Bitnami | All versions | 3.6.14, 3.7.11, 3.8.10, 3.9.5, 3.10.1 | | `platform-python` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.8-39.el8_4 | | `platform-python-debug` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.8-39.el8_4 | | `platform-python-devel` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.8-39.el8_4 | | `python3-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.8-39.el8_4 | | `python3-debugsource` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.8-39.el8_4 | | `python3-idle` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.8-39.el8_4 | | `python3-test` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.8-39.el8_4 | | `python3-tkinter` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.8-39.el8_4 | | `platform-python` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.8-39.el8_4 | | `python3` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.8-39.el8_4 | | `python3-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.8-39.el8_4 | | `python3-debugsource` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.8-39.el8_4 | | `python3-libs` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.8-39.el8_4 | | `python3-test` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.8-39.el8_4 | Products: Fedoraproject Extra Packages for Enterprise Linux, Fedoraproject Fedora, Netapp Hci Compute Node Firmware, Netapp Management Services for Element Software and Netapp Hci, Netapp Ontap Select Deploy Administration Utility, Netapp Solidfire\, Enterprise Sds \& Hci Storage Node, Python Python, Redhat Codeready Linux Builder, Redhat Codeready Linux Builder for Ibm Z Systems, Redhat Codeready Linux Builder for Power Little Endian, Redhat Enterprise Linux, Redhat Enterprise Linux Eus, Redhat Enterprise Linux for Ibm Z Systems, Redhat Enterprise Linux for Ibm Z Systems Eus, Redhat Enterprise Linux for Power Little Endian, Redhat Enterprise Linux for Power Little Endian Eus, Redhat Enterprise Linux Server Aus, Redhat Enterprise Linux Server for Power Little Endian Update Services for Sap Solutions, Redhat Enterprise Linux Server Tus, Redhat Enterprise Linux Server Update Services for Sap Solutions. ## How do I fix CVE-2021-3733? Upgrade libpython to a fixed version for your release line: 3.6.14, 3.7.11, 3.8.10 or 3.9.5. ## Is CVE-2021-3733 being exploited? There is no known exploitation of CVE-2021-3733 in the wild and no public exploit code. ## Other vulnerabilities in Fedoraproject Extra Packages for Enterprise Linux - [CVE-2023-34152](https://insights.sbomify.com/CVE-2023-34152/): Command injection in ImageMagick (critical 9.8) - [CVE-2022-4170](https://insights.sbomify.com/CVE-2022-4170/): Code injection in rxvt-unicode (critical 9.8) - [CVE-2022-40315](https://insights.sbomify.com/CVE-2022-40315/): Moodle Minor SQL injection risk in admin user browsing (critical 9.8) - [CVE-2022-45152](https://insights.sbomify.com/CVE-2022-45152/): Moodle blind Server-Side Request Forgery (SSRF) vulnerability in LTI provider library (critical 9.1) - [CVE-2022-24882](https://insights.sbomify.com/CVE-2022-24882/): Server side NTLM does not properly check parameters in FreeRDP (critical 9.1) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-3733 and fix it if it is affected. What it is: CVE-2021-3733 is a medium-severity denial of service vulnerability in Fedoraproject Extra Packages for Enterprise Linux, published on 7 Mar 2022. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-3733 in the wild and no public exploit code. Affected packages and fixed versions: - libpython (Bitnami): affected all versions; fixed in 3.6.14, 3.7.11, 3.8.10, 3.9.5 - python (Bitnami): affected all versions; fixed in 3.6.14, 3.7.11, 3.8.10, 3.9.5 - python-min (Bitnami): affected all versions; fixed in 3.6.14, 3.7.11, 3.8.10, 3.9.5, 3.10.1 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-3733/ (Markdown: https://insights.sbomify.com/CVE-2021-3733/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3733 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3733 - OSV: https://osv.dev/vulnerability/CVE-2021-3733 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-3733/ Summaries are generated and may contain mistakes; the official description above is the record.