CVE-2021-33503

mediumpriority · track · 31EPSS 0.033 · 88 %ileDEEURUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

3.27% (88th) EPSS

CVSS 5 · medium

Is it mine?

25 products

Check your exposure

Who says so?

6 sources

cnnvd · enisa_euvd · fstec_bdu · osv

EPSS · scored 2026-10-27

An issue was discovered in urllib3 before 1.26.5. When provided with a URL containing many @ characters in the authority component, the authority regular expression exhibits catastrophic backtracking, causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect.

cvss

Technical severity, 0–10. One row per scoring source.

7.5

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 5–7.5

v2.05mediumAV:N/AC:L/Au:N/C:N/I:N/A:Pprimary · NVD / NIST USexploitability 10 · impact 2.9

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hprimary · NVD / NIST USexploitability 3.9 · impact 3.6

v3.17.5highAV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsecondary · FSTEC (BDU) RU

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsecondary · OSV

v3.16.9mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:Usecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-400USprimaryCWE-400USCWE-400US

affected products (25)

Products and version ranges known to be affected.

Dell ECS <3.8.1.0all versionscert_bundDE
Dell PowerEdgeall versionscert_bundDEcpe:/h:dell:poweredge:-
IBM InfoSphere Information Serverall versionscert_bundDEcpe:/a:ibm:infosphere_information_server:-
IBM QRadar SIEM 7.3all versionscert_bundDEcpe:/a:ibm:qradar_siem:7.3
IBM QRadar SIEM 7.4all versionscert_bundDEcpe:/a:ibm:qradar_siem:7.4
IBM QRadar SIEM 7.5.0all versionscert_bundDEcpe:/a:ibm:qradar_siem:7.5.0
Dell ECS< 3.8.1.0cert_bundDE
n/a n/a≤ n/aenisa_euvdEU
Andrey Petrov urllib3≤ 1.26.5fstec_bduRU
Fedora Project Fedora≤ 34fstec_bduRU
Fedora Project Fedora≤ 33fstec_bduRU
IBM Corp. IBM Qradar Advisor≤ 2.6.2fstec_bduRU
АО «НППКТ» ОСОН ОСнова Оnyx≤ 2.8fstec_bduRU
АО «НТЦ ИТ РОСА» ROSA Virtualization 3.0≤ 3.0fstec_bduRU
ООО «РусБИТех-Астра» Astra Linux Special Edition≤ 1.7fstec_bduRU
ФССП России ОС ТД АИС ФССП России≤ ИК6fstec_bduRU
fedoraproject fedora= 33nvdUScpe:2.3:o:fedoraproject:fedora:*:*:*:*:*:*:*:*
fedoraproject fedora= 34nvdUScpe:2.3:o:fedoraproject:fedora:*:*:*:*:*:*:*:*
oracle enterprise manager ops center= 12.4.0.0nvdUScpe:2.3:a:oracle:enterprise_manager_ops_center:*:*:*:*:*:*:*:*
oracle instantis enterprisetrack= 17.1nvdUScpe:2.3:a:oracle:instantis_enterprisetrack:*:*:*:*:*:*:*:*

showing 20 of 25

advisories (6)

Vendor and ecosystem advisories describing this.

WID-SEC-W-2023-0156Red Hat OpenShift: Schwachstelle ermöglicht Denial of ServiceDeutsch2021-09-08csaf · cert_bundDE
Ein entfernter, anonymer Angreifer kann eine Schwachstelle in Red Hat OpenShift ausnutzen, um einen Denial of Service Angriff durchzuführen.
WID-SEC-W-2023-1350Splunk Splunk Enterprise: Mehrere Schwachstellen in Komponenten von DrittanbieternDeutsch2023-06-01csaf · cert_bundDE
Ein Angreifer kann mehrere Schwachstellen in Splunk Splunk Enterprise in diversen Komponenten von Drittanbietern ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen.
WID-SEC-W-2024-0794Dell ECS: Mehrere SchwachstellenDeutsch2024-04-04csaf · cert_bundDE
Ein Angreifer kann mehrere Schwachstellen in Dell ECS ausnutzen, um seine Privilegien zu erweitern, beliebigen Programmcode mit Administratorrechten auszuführen, Informationen offenzulegen, Dateien zu manipulieren, einen Cross-Site-Scripting-Angriff durchzuführen, Sicherheitsvorkehrungen zu umgehen oder einen Denial of Service Zustand herbeizuführen.
WID-SEC-W-2025-0227IBM QRadar SIEM: Mehrere SchwachstellenDeutsch2021-11-30csaf · cert_bundDE
Ein entfernter, authentisierter Angreifer kann mehrere Schwachstellen in IBM QRadar SIEM ausnutzen, um seine Privilegien zu erweitern, Administratorrechte zu erlangen, beliebigen Programmcode auszuführen, Informationen offenzulegen, Dateien zu manipulieren oder Sicherheitsvorkehrungen zu umgehen.
GHSA-q2q7-5pp4-w6pgCatastrophic backtracking in URL authority parser when passed URL containing many @ characters2021-06-01ghsa · osvUS
### Impact When provided with a URL containing many `@` characters in the authority component the authority regular expression exhibits catastrophic backtracking causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect. ### Patches The issue has been fixed in urllib3 v1.26.5. ### References - [CVE-2021-33503](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-33503) - [JVNVU#92413403 (English)](https://jvn.jp/en/vu/JVNVU92413403/) - [JVNVU#92413403 (Japanese)](https://jvn.jp/vu/JVNVU92413403/) - [urllib3 v1.26.5](https://github.com/urllib3/urllib3/releases/tag/1.26.5) ### For more information If you have any questions or comments about this advisory: * Ask in our [community Discord](https://discord.gg/urllib3) * Email [sethmichaellarson@gmail.com](mailto:sethmichaellarson@gmail.com)
PYSEC-2021-1082021-06-29vendor · osvUS
An issue was discovered in urllib3 before 1.26.5. When provided with a URL containing many @ characters in the authority component, the authority regular expression exhibits catastrophic backtracking, causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect.

also known as (7)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu osv cert_bund nvd NVD CVE.org MITRE

published 2021-06-29modified 2026-06-17

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+9606 more

references (42)

External citations — patches, advisories, analysis.

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