How severe is CVE-2021-4164?

CVE-2021-4164 has a CVSS score of 8.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-4164?

CVE-2021-4164 affects the following packages: calibreweb (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2021-4164?

Update calibreweb to 0.6.15 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-4164 is resolved across your whole dependency graph.

How do I detect CVE-2021-4164 in my PyPI dependencies?

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

How do I mitigate CVE-2021-4164 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2021-4164 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-4164, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-4164?

CVE-2021-4164 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 44th 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-2021-4164?

CVE-2021-4164 is classified as Cross-Site Request Forgery (CSRF) (CWE-352). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-4164 published, and has it been updated?

CVE-2021-4164 was published on January 17, 2022 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2021-4164 — calibreweb

HIGHFix: janeczku/calibre-web@785726d

CVE-2021-4164 is a high-severity (CVSS 8.8) Cross-Site Request Forgery (CSRF) vulnerability in calibreweb. 1 public exploit reference exists, so weaponization risk is real. A fix is available for calibreweb — see the affected versions and patch details below.

calibre-web is vulnerable to Cross-Site Request Forgery (CSRF)

Also known asGHSA-wxr6-29pv-ch68PYSEC-2026-621

Published

Jan 17, 2022

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs44th percentile — riskier than 44% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-4164 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐍calibreweb

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

Description

calibre-web is vulnerable to Cross-Site Request Forgery (CSRF)

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`calibreweb`	all versions	0.6.15`pip install --upgrade 'calibreweb==0.6.15'`

Affected Products

1 product · 1 configurations

Application

calibre-webjaneczku

< 0.6.15

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

calibre-web is vulnerable to Cross-Site Request Forgery (CSRF)

huntr.devNVDJan 2022

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for calibreweb, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update calibreweb to 0.6.15 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-4164 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

calibre-web is vulnerable to Cross-Site Request Forgery (CSRF)

O3 Security · Impact-Aware SCA

Is CVE-2021-4164 in your dependencies?

Find it across PyPI, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

8.8/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Raw vector

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

CWE Classification

CWE-352Cross-Site Request Forgery (CSRF)

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

calibre-web

4.0/10

Code-Review1/10

Maintained10/10

Branch-Protection0/10

Assessed Oct 5, 2026

Timeline

Disclosed

Jan 17, 2022

First exploit

Jan 22, 2022

5 days after disclosure — rapid exploitation

Last updated

Jul 9, 2026

Identifiers

CVE-2021-4164

GHSA-wxr6-29pv-ch68

PYSEC-2026-621

References

Advisorynvd.nist.gov Fixgithub.com Packagegithub.com Evidencehuntr.dev

Related vulnerabilities

This CVE is high severity; 1 of 8 other CVEs affecting calibreweb is rated as high or higher (top: high).

CVE-2025-65858CVE-2025-6998CVE-2025-7404CVE-2021-3987CVE-2021-3986CVE-2021-3988CVE-2024-39123CVE-2022-2525

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 9, 2026

CVE-2021-4164 — calibreweb

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-4164 in your dependencies?