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Vulnerabilities

Vulnerability · CVE-2021-3733

There's a flaw in urllib's AbstractBasicAuthHandler class.

Published Mar 10, 2022 · catalog updated Oct 14, 2026 · There's a flaw in

Check if you run it

No confirmed exploitation is on record for CVE-2021-3733. EPSS is 4.80%. Act only if a listed version of There's a flaw in is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (There's a flaw in).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
4.80%
Remediation
Advisory link
Affected products
cpe fedoraproject/extra packages for enterprise linux · cpe netapp/management services for element software and netapp hci · cpe python/python · cpe redhat/codeready linux builder · cpe redhat/codeready linux builder for ibm z systems · cpe redhat/codeready linux builder for power little endian

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe fedoraproject/extra packages for enterprise linux7.0
  • cpe netapp/management services for element software and netapp hciversion unspecified
  • cpe python/python3.10.0
  • cpe redhat/codeready linux builder8.0
  • cpe redhat/codeready linux builder for ibm z systems8.0
  • cpe redhat/codeready linux builder for power little endian8.0

How to fix CVE-2021-3733

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2021-3733. EPSS is 4.80%. Act only if a listed version of There's a flaw in is installed.

Which versions are affected?

Compare what you have installed with fedoraproject/extra packages for enterprise linux 7.0; 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. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-400: Uncontrolled Resource Consumption. EPSS 4.80%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 10, 2022 · NIST NVD

    Detected

    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 availabil

  2. Oct 14, 2026 · NIST NVD

    Updated

    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 availabil

Sources

  • CVE.orgVulnerability recordCVE-2021-3733

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2021-3733

    30-day exploitation probability 4.8%

    first.org
  • NIST NVDVulnerability recordCVE-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 crafte

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 16, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.