How severe is CVE-2021-3785?

CVE-2021-3785 has a CVSS score of 5.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-3785?

CVE-2021-3785 affects the following packages: yourls/yourls (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-3785?

Update yourls/yourls to 1.8.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3785 is resolved across your whole dependency graph.

How do I detect CVE-2021-3785 in my Packagist dependencies?

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

How do I mitigate CVE-2021-3785 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2021-3785 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-3785, 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-2021-3785?

CVE-2021-3785 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 54th 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-2021-3785?

CVE-2021-3785 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2021-3785 published, and has it been updated?

CVE-2021-3785 was published on September 15, 2021 and was last updated on October 20, 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

MEDIUM severity

CVE-2021-3785 — yourls

MEDIUMFix: yourls/yourls@1d8e224

CVE-2021-3785 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in yourls/yourls. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for yourls/yourls — see the affected versions and patch details below.

Cross-site Scripting in yourls

Also known asGHSA-m9fq-c9hp-59g7

Published

Sep 15, 2021

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

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

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs54th percentile — riskier than 54% of all scored CVEsHighest risk

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐘yourls/yourls

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

yourls is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in edit dialog.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`yourls/yourls`	all versions	1.8.2`composer require yourls/yourls:^1.8.2`

Affected Products

1 product · 1 configurations

Application

yourlsyourls

< 1.8.2

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.

yourls is vulnerable to Improper Neutralization of Input During Web Page…

huntr.devNVDSep 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for yourls/yourls, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update yourls/yourls to 1.8.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3785 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

yourls is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in edit dialog.

O3 Security · Impact-Aware SCA

Is CVE-2021-3785 in your dependencies?

Find it across Packagist, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

5.4/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Raw vector

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

CWE Classification

CWE-79Cross-site Scripting (XSS)

Weaponization

No Nuclei template or Metasploit module yet. 1 public proof-of-concept reference is listed on this page.

Timeline

Disclosed

Sep 15, 2021

First exploit

Sep 23, 2021

Last updated

Oct 20, 2026

Identifiers

CVE-2021-3785

GHSA-m9fq-c9hp-59g7

References

Advisorynvd.nist.gov · CVE 2021 3785 Fixgithub.com · 1d8e224ebabb8a4c75b97f026950ed710faab0ff Fixhuntr.dev · b4085d13 54fa 4419 a2ce 1d780cc31638 Packagegithub.com · yourls

Related vulnerabilities

This CVE is medium severity; 7 of 8 other CVEs affecting yourls/yourls are rated as high or higher (top: critical).

CVE-2026-62858CVE-2026-63135GHSA-6mp4-q625-mxjpCVE-2020-27388CVE-2022-0088CVE-2021-3783CVE-2021-3734CVE-2019-14537

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 20, 2026