CVE-2021-3856Network attack vector

Authenticated file disclosure via theme path traversal

Published Aug 26, 2022 · Updated Aug 3, 2024

Path traversal in Keycloak before 15.1.0 allows remote authenticated users to read classloader resources through theme requests. ClassLoaderTheme and ClasspathThemeResourceProviderFactory append a caller-controlled relative path to a resource root and open the resulting classloader URL without verifying that it remains beneath that root. Low-privileged network access is required, and disclosure is limited to resources available to the server classloader.

CVSS severity4.3
Medium
EPSS probability1.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path traversal in Keycloak before 15.1.0 allows remote authenticated users to read classloader resources through theme requests. ClassLoaderTheme and ClasspathThemeResourceProviderFactory append a caller-controlled relative path to a resource root and open the resulting classloader URL without verifying that it remains beneath that root. Low-privileged network access is required, and disclosure is limited to resources available to the server classloader.

The record

CVE
CVE-2021-3856
Published
Aug 26, 2022
Updated
Aug 3, 2024
Vendor
Keycloak
Product
Keycloak
Classifications
CWE-552, CWE-22, T1005
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 26, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=Fixed in 15.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Keycloak · Keycloakversion=Fixed in 15.1.0

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/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.

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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-552Files or Directories Accessible to External Parties
CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1005Data from Local System

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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