CVE-2026-24400

CVE-2026-24400 is a high-severity XML external entity injection (XXE) vulnerability in org.assertj:assertj-core (maven), affecting versions >= 1.4.0, <= 3.27.6. It is fixed in 3.27.7.

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Summary

AssertJ has XML External Entity (XXE) vulnerability when parsing untrusted XML via isXmlEqualTo assertion

An XML External Entity (XXE) vulnerability exists in org.assertj.core.util.xml.XmlStringPrettyFormatter: the toXmlDocument(String) method initializes DocumentBuilderFactory with default settings, without disabling DTDs or external entities. This formatter is used by the isXmlEqualTo(CharSequence) assertion for CharSequence values.

An application is vulnerable only when it uses untrusted XML input with one of the following methods:

  • isXmlEqualTo(CharSequence) from org.assertj.core.api.AbstractCharSequenceAssert
  • xmlPrettyFormat(String) from org.assertj.core.util.xml.XmlStringPrettyFormatter

Mitigation

isXmlEqualTo(CharSequence) has been deprecated in favor of XMLUnit in version 3.18.0 and will be removed in version 4.0. Users of affected versions should, in order of preference:

  1. Replace isXmlEqualTo(CharSequence) with XMLUnit, or
  2. Upgrade to version 3.27.7, or
  3. Avoid using isXmlEqualTo(CharSequence) or XmlStringPrettyFormatter with untrusted input.

XmlStringPrettyFormatter has historically been considered a utility for isXmlEqualTo(CharSequence) rather than a feature for AssertJ users, so it is deprecated in version 3.27.7 and removed in version 4.0, with no replacement.

References

Impact

If untrusted XML input is processed by the methods mentioned above (e.g., in test environments handling external fixture files), an attacker could:

  • Read arbitrary local files via file:// URIs (e.g., /etc/passwd, application configuration files)
  • Perform Server-Side Request Forgery (SSRF) via HTTP/HTTPS URIs
  • Cause Denial of Service via "Billion Laughs" entity expansion attacks

An XML parser processes external entity references in untrusted input, causing the server to fetch internal resources or remote URLs. Typical impact: local file disclosure, server-side request forgery, or denial of service.

Affected versions

org.assertj:assertj-core (>= 1.4.0, <= 3.27.6)

Security releases

org.assertj:assertj-core → 3.27.7 (maven)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

Upgrade org.assertj:assertj-core to 3.27.7 or later to resolve this vulnerability.

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

  1. What is CVE-2026-24400? CVE-2026-24400 is a high-severity XML external entity injection (XXE) vulnerability in org.assertj:assertj-core (maven), affecting versions >= 1.4.0, <= 3.27.6. It is fixed in 3.27.7. An XML parser processes external entity references in untrusted input, causing the server to fetch internal resources or remote URLs.
  2. Which versions of org.assertj:assertj-core are affected by CVE-2026-24400? org.assertj:assertj-core (maven) versions >= 1.4.0, <= 3.27.6 is affected.
  3. Is there a fix for CVE-2026-24400? Yes. CVE-2026-24400 is fixed in 3.27.7. Upgrade to this version or later.
  4. Is CVE-2026-24400 exploitable, and should I be worried? Whether CVE-2026-24400 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
  5. What actually determines whether CVE-2026-24400 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
  6. How do I fix CVE-2026-24400? Upgrade org.assertj:assertj-core to 3.27.7 or later.

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