How severe is CVE-2021-21339?

CVE-2021-21339 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-21339?

CVE-2021-21339 affects the following packages: typo3/cms-core (Packagist), typo3/cms-core (Packagist), typo3/cms-core (Packagist), typo3/cms-core (Packagist), typo3/cms-core (Packagist), typo3/cms-core (Packagist), typo3/cms (Packagist), typo3/cms (Packagist), and 1 more. Ecosystems affected: Packagist.

How do I fix CVE-2021-21339?

Update typo3/cms-core to 6.2.57 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21339 is resolved across your whole dependency graph.

How do I detect CVE-2021-21339 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for typo3/cms-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-21339 if there is no patch (or I can't update yet)?

Until you can upgrade, make sure every query built from user input uses parameterised statements or a prepared-statement API rather than string concatenation, and reduce the database account's privileges so an injected query cannot read or alter data beyond what the feature needs.

Is CVE-2021-21339 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-21339 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-21339?

CVE-2021-21339 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 59th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-21339?

CVE-2021-21339 is classified as CWE-312 (CWE-312). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-21339 published, and has it been updated?

CVE-2021-21339 was published on March 23, 2021 and was last updated on August 27, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

Not in CISA KEV

HIGH severity

CVE-2021-21339 — cms-core

HIGH

CVE-2021-21339 is a high-severity (CVSS 7.5) CWE-312 vulnerability in typo3/cms-core. A fix is available for typo3/cms-core — see the affected versions and patch details below.

Cleartext storage of session identifier

Also known asBIT-typo3-2021-21339GHSA-qx3w-4864-94ch

Published

Mar 23, 2021

Updated

Aug 27, 2026

Affected

9 pkgs

Patched

9 / 9

Exploits

None indexed

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs59th percentile — riskier than 59% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-21339 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

9 pkgs affected

🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms🐘typo3/cms+1 more

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

Problem

User session identifiers were stored in cleartext - without processing of additional cryptographic hashing algorithms. This vulnerability cannot be exploited directly and occurs in combination with a chained attack - like for instance SQL injection in any other component of the system.

Solution

Update to TYPO3 versions 6.2.57, 7.6.51, 8.7.40, 9.5.25, 10.4.14, 11.1.1 that fix the problem described.

Credits

Thanks to TYPO3 security team member Oliver Hader who reported this issue and to TYPO3 core & security team members Benni Mack & Oliver Hader who fixed the issue.

References

TYPO3-CORE-SA-2021-006

Affected Packages

9 total 9 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`typo3/cms-core`	≥ 6.2.0&&< 6.2.57	6.2.57`composer require typo3/cms-core:^6.2.57`
🐘Packagist	`typo3/cms-core`	≥ 7.0.0&&< 7.6.51	7.6.51`composer require typo3/cms-core:^7.6.51`
🐘Packagist	`typo3/cms-core`	≥ 8.0.0&&< 8.7.40	8.7.40`composer require typo3/cms-core:^8.7.40`
🐘Packagist	`typo3/cms-core`	≥ 10.0.0&&< 10.4.14	10.4.14`composer require typo3/cms-core:^10.4.14`
🐘Packagist	`typo3/cms-core`	≥ 11.0.0&&< 11.1.1	11.1.1`composer require typo3/cms-core:^11.1.1`
🐘Packagist	`typo3/cms-core`	≥ 9.0.0&&< 9.5.25	9.5.25`composer require typo3/cms-core:^9.5.25`

Affected Products

1 product · 6 configurations

Application

typo3typo3

≥ 11.0.0 && < 11.1.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for typo3/cms-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update typo3/cms-core to 6.2.57 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21339 is resolved across your whole dependency graph.
Workarounds
Until you can upgrade, make sure every query built from user input uses parameterised statements or a prepared-statement API rather than string concatenation, and reduce the database account's privileges so an injected query cannot read or alter data beyond what the feature needs.

Frequently Asked Questions

### Problem User session identifiers were stored in cleartext - without processing of additional cryptographic hashing algorithms. This vulnerability cannot be exploited directly and occurs in combination with a chained attack - like for instance SQL injection in any other component of the system. ### Solution Update to TYPO3 versions 6.2.57, 7.6.51, 8.7.40, 9.5.25, 10.4.14, 11.1.1 that fix the problem described. ### Credits Thanks to TYPO3 security team member Oliver Hader who reported this issue and to TYPO3 core & security team members Benni Mack & Oliver Hader who fixed the issue. ###

O3 Security · Impact-Aware SCA

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CVSS Score

7.5/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CWE Classification

CWE-312CWE-312

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

TYPO3.CMS

6.0/10

Code-Review10/10

Maintained10/10

Branch-Protection0/10

Assessed Oct 5, 2026

Timeline

Disclosed

Mar 23, 2021

Last updated

Aug 27, 2026

Identifiers

CVE-2021-21339

GHSA-qx3w-4864-94ch

BIT-typo3-2021-21339

References

Advisorygithub.com Advisorypackagist.org Advisorytypo3.org Advisorynvd.nist.gov Webgithub.com Webgithub.com

Related vulnerabilities

This CVE is high severity; 3 of 8 other CVEs affecting typo3/cms-core are rated as high or higher (top: high).

CVE-2026-19418CVE-2026-47352CVE-2026-47347CVE-2026-47343CVE-2026-49740CVE-2026-47348CVE-2026-49742CVE-2026-47349

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedAug 27, 2026

CVE-2021-21339 — cms-core

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Problem

Solution

Credits

References

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-21339 in your dependencies?