How severe is CVE-2018-20677?

CVE-2018-20677 has a CVSS score of 6.1/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2018-20677?

CVE-2018-20677 affects the following packages: org.webjars:bootstrap (Maven), bootstrap (npm), bootstrap-sass (npm), bootstrap (NuGet), twbs/bootstrap (Packagist), bootstrap (RubyGems), bootstrap-sass (RubyGems). Ecosystems affected: Maven, npm, NuGet, Packagist, RubyGems.

How do I fix CVE-2018-20677?

Update org.webjars:bootstrap to 3.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-20677 is resolved across your whole dependency graph.

How do I detect CVE-2018-20677 in my Maven, npm, NuGet, Packagist, RubyGems dependencies?

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

How do I mitigate CVE-2018-20677 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-2018-20677 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2018-20677, 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-2018-20677?

CVE-2018-20677 has an EPSS (Exploit Prediction Scoring System) score of 4.0%, placing it in the 91th 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-2018-20677?

CVE-2018-20677 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-2018-20677 published, and has it been updated?

CVE-2018-20677 was published on January 9, 2019 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.

☕

☕ Maven📦 npm.NET NuGet🐘 Packagist💎 RubyGems

Not in CISA KEV

MEDIUM severity

CVE-2018-20677 — bootstrap

MEDIUMFix: twbs/bootstrap#27047

CVE-2018-20677 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in org.webjars:bootstrap. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for org.webjars:bootstrap — see the affected versions and patch details below.

bootstrap Cross-site Scripting vulnerability

Also known asGHSA-ph58-4vrj-w6hr

Published

Jan 9, 2019

Updated

Oct 20, 2026

Affected

7 pkgs

Patched

7 / 7

Exploits

1 known

Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

4.0%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs91th percentile — riskier than 91% 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

7 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

15Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

bootstrapnpm

8.3Mdownloads / week

bootstrap-sassnpm

376Kdownloads / week

Description

In Bootstrap before 3.4.0, XSS is possible in the affix configuration target property.

Affected Packages

7 total 7 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.webjars:bootstrap`	all versions	3.4.0`org.webjars:bootstrap:3.4.0`
📦npm	`bootstrap`	all versions	3.4.0`npm install bootstrap@3.4.0`
📦npm	`bootstrap-sass`	all versions	3.4.0`npm install bootstrap-sass@3.4.0`
.NETNuGet	`bootstrap`	all versions	3.4.0`dotnet add package bootstrap --version 3.4.0`
🐘Packagist	`twbs/bootstrap`	all versions	3.4.0`composer require twbs/bootstrap:^3.4.0`
💎RubyGems	`bootstrap`	all versions	3.4.0`bundle update bootstrap --conservative`

Affected Products

1 product · 1 configurations

Application

bootstrapgetbootstrap

< 3.4.0

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.

In Bootstrap before 3.4.0, XSS is possible in the affix configuration ta…

github.comNVDJul 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.webjars:bootstrap, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.webjars:bootstrap to 3.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-20677 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.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Red Hat CloudForms 4.6 and newer versions include the vulnerable component, but there is no risk of exploitation, since there is no possible vector to access the vulnerability. Older Red Hat CloudForms versions do not use the vulnerable component at all. Red Hat Virtualization 4.2 EUS contains the affected version of…

Product	Fixed in	Advisory
Red Hat Decision Manager 7	see advisory	RHSA-2020:0133
Red Hat Enterprise Linux 7	`ipa-0:4.6.8-5.el7`	RHSA-2020:3936
Red Hat Enterprise Linux 8	`idm:client-8030020200923172426.05ac3f11`	RHSA-2020:4670
Red Hat OpenStack Platform 13.0 (Queens)	`python-XStatic-Bootstrap-SCSS-0:3.4.1.0-1.el7ost`	RHSA-2020:5571
Red Hat Process Automation 7	see advisory	RHSA-2020:0132
Red Hat Single Sign-On 7.3.2 zip	`bootstrap`	RHSA-2019:1456
Red Hat Virtualization Engine 4.3	`ovirt-engine-api-explorer-0:0.0.4-1.el7ev`	RHBA-2019:1076
Red Hat Virtualization Engine 4.3	`ovirt-engine-api-explorer-0:0.0.5-1.el7ev`	RHBA-2019:1570

Frequently Asked Questions

In Bootstrap before 3.4.0, XSS is possible in the affix configuration target property.

O3 Security · Impact-Aware SCA

Is CVE-2018-20677 in your dependencies?

Find it across Maven, npm, NuGet, including transitive dependencies.

Scan my dependencies How O3 SCA works