How severe is CVE-2021-3879?

CVE-2021-3879 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-2021-3879?

CVE-2021-3879 affects the following packages: snipe/snipe-it (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-3879?

Update snipe/snipe-it to 5.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3879 is resolved across your whole dependency graph.

How do I detect CVE-2021-3879 in my Packagist dependencies?

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

How do I mitigate CVE-2021-3879 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-2021-3879 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-3879, 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-2021-3879?

CVE-2021-3879 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 56th 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-2021-3879?

CVE-2021-3879 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-2021-3879 published, and has it been updated?

CVE-2021-3879 was published on October 19, 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

MEDIUM severity

CVE-2021-3879 — snipe-it

MEDIUMFix: snipe/snipe-it@bda23bb

CVE-2021-3879 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in snipe/snipe-it. 1 public exploit reference exists, so weaponization risk is real. A fix is available for snipe/snipe-it — see the affected versions and patch details below.

Cross-site Scripting in snipe-it

Also known asGHSA-9g3v-j3cr-6fc6

Published

Oct 19, 2021

Updated

Aug 27, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Sep 30, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs56th percentile — riskier than 56% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-3879 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

🐘snipe/snipe-it

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

snipe-it is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`snipe/snipe-it`	all versions	5.3.0`composer require snipe/snipe-it:^5.3.0`

Affected Products

1 product · 1 configurations

Application

snipe-itsnipeitapp

< 5.3.0

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.

snipe-it is vulnerable to Improper Neutralization of Input During Web Pa…

huntr.devNVDOct 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for snipe/snipe-it, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update snipe/snipe-it to 5.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3879 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

snipe-it is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

O3 Security · Impact-Aware SCA

Is CVE-2021-3879 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 known public exploit tooling found.

OpenSSF Scorecard

Package health score

snipe-it

6.3/10

Maintained10/10

Code-Review3/10

Branch-ProtectionN/A

Assessed Sep 28, 2026

Timeline

Disclosed

Oct 19, 2021

First exploit

Oct 21, 2021

2 days after disclosure — rapid exploitation

Last updated

Aug 27, 2026

Identifiers

CVE-2021-3879

GHSA-9g3v-j3cr-6fc6

References

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

Related vulnerabilities

This CVE is medium severity; 8 of 8 other CVEs affecting snipe/snipe-it are rated as high or higher (top: high).

CVE-2026-55515CVE-2026-55476CVE-2026-55516CVE-2026-55475CVE-2026-55479CVE-2026-55472CVE-2026-55474CVE-2026-55478

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedAug 27, 2026