CVE-2021-24759

PDF.js Viewer <= 2.0.1 - Authenticated (Contributor+) Stored Cross-Site Scripting

2021-08-11 00:00

Strategic Overview

Status: Patched in 2.0.2
Affected Plugin: PDF.js Viewer
Affected Version: < 2.0.2
CVSS: 5.4Medium
Weakness type: CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVE: CVE-2021-24759

At a glance

CVE-2021-24759 is a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the PDF.js Viewer WordPress plugin, affecting versions < 2.0.2. It carries a CVSS score of 5.4 (reachable over the network; low attack complexity). Exploitation requires an authenticated account at Contributor level or above. The issue is fixed in version 2.0.2; sites on affected versions should update now. Disclosed August 2021, reported by apple502j.

Vulnerability Overview

The PDF.js Viewer WordPress plugin before 2.0.2 does not escape some of its shortcode and Gutenberg Block attributes, which could allow users with a role as low as Contributor to to perform Cross-Site Scripting attacks

Technical Analysis

The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no interaction from a victim user.

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Reaching this weakness in PDF.js Viewer < 2.0.2 takes an account at Contributor level or above. Cross-site scripting happens when input from a request is written into a page without being escaped for the context it lands in, so the browser parses attacker-supplied text as markup or script.

Injected script runs with the privileges of whoever views the affected page, which is how these flaws turn into administrator session theft, silent account creation or persistent backdoors in page content. For PDF.js Viewer the fix is 2.0.2: builds < 2.0.2 are affected, anything from 2.0.2 onward is not.

Remediation

Update to version 2.0.2, or a newer patched version

How does WordSec protect against this?

An attacker needs Contributor access first, so the firewall sees the attempt as traffic from a logged-in account: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: PDF.js Viewer 2.0.2 closes this, and updating the plugin is the step that ends it.

Firewall
Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2021-24759 https://www.wordfence.com/threat-intel/vulnerabilities/id/d608a4c0-14ba-4801-aa5a-0b4dab0acd65 https://nvd.nist.gov/vuln/detail/CVE-2021-24759

Related records

Same weakness class

CVSS Vector

5.4

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

Base

Attack VectorNetwork
Attack ComplexityLow
Privileges RequiredLow
User InteractionNone
ScopeUnchanged
ConfidentialityLow
IntegrityLow
AvailabilityNone

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