CVE-2020-8155Network attack vector

Authenticated script execution via malicious PDF rendering

Published May 12, 2020 · Updated Aug 4, 2024

Cross-site scripting in the Files PDF viewer in Nextcloud Server 18.0.3 allows remote authenticated users to execute script via a malicious PDF. The viewer embeds an outdated PDF.js build that processes attacker-supplied PDF content without safely containing script execution in the victim's browser. Exploitation requires an authenticated attacker to supply the file and a user to open it, exposing or modifying data available to that user's session.

CVSS severity5.4
Medium
EPSS probability1.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in the Files PDF viewer in Nextcloud Server 18.0.3 allows remote authenticated users to execute script via a malicious PDF. The viewer embeds an outdated PDF.js build that processes attacker-supplied PDF content without safely containing script execution in the victim's browser. Exploitation requires an authenticated attacker to supply the file and a user to open it, exposing or modifying data available to that user's session.

The record

CVE
CVE-2020-8155
Published
May 12, 2020
Updated
Aug 4, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Server
Classifications
CWE-79, T1204.002
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 12, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=18.0.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Serverversion=18.0.3

Published CVSS scores

3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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