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…
- 6.5MediumCVSS base score
- 4.8%Exploitation in 30 daysEPSS · top 7.9% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By redhat
- 7 months later
· 7 months later
Published
- 5 years later
· 5 years later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| NVDNVD · Modified | 3.1 | Medium6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 4.8% · top 7.9% of all CVEs (11 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.5.
Affected products
python
- affected Fixed in python v3.6.14, python v3.7.11, python v3.8.10, python v3.9.5.
References
References10
- https://bugs.python.org/issue43075 (opens in a new tab)x_transferred
- https://bugzilla.redhat.com/show_bug.cgi?id=1995234 (opens in a new tab)x_transferred
- https://github.com/python/cpython/pull/24391 (opens in a new tab)x_transferred
- https://ubuntu.com/security/CVE-2021-3733 (opens in a new tab)x_transferred
- https://github.com/python/cpython/commit/7215d1ae25525c92b026166f9d5cac85fb (opens in a new tab)x_transferred
- https://security.netapp.com/advisory/ntap-20220407-0001/ (opens in a new tab)x_transferred
- [debian-lts-announce] 20230524 [SECURITY] [DLA 3432-1] python2.7 security update (opens in a new tab)mailing-listx_transferred
- [debian-lts-announce] 20230630 [SECURITY] [DLA 3477-1] python3.7 security update (opens in a new tab)mailing-listx_transferred
- https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html (opens in a new tab)
- https://cert-portal.siemens.com/productcert/html/ssa-398330.html (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2021-27010 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2021-3733)Record last updated .