CVE-2024-55875: http4k has a potential XXE (XML External Entity Injection) vulnerability

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 1.9%, percentile 80: FIRST’s model estimates a 1.9% chance of exploitation activity in the next 30 days, higher than 80% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes org.http4k:http4k-format-xml (Maven) < 6.50.0.0, fixed in 6.50.0.0. Check your lockfile, including transitive dependencies.

What it is

http4k is a functional toolkit for Kotlin HTTP applications. Prior to version 6.50.0.0, there is a potential XXE (XML External Entity Injection) vulnerability when http4k handling malicious XML contents within requests, which might allow attackers to read local sensitive information on server, trigger Server-side Request Forgery and even execute code under some circumstances. The original fix shipped in v5.41.0.0 / v4.50.0.0 closed the documented external-entity attack class (SSRF, local-file disclosure, code execution) by setting ACCESSEXTERNALDTD="", ACCESSEXTERNALSCHEMA="", and isExpandEntityReferences=false on the default DocumentBuilderFactory. A residual gap remained: the parser still accepted documents containing declarations even though external entity resolution was blocked. This left open billion-laughs-style internal entity expansion DoS attacks against any application using Body.xml() or Document.asXmlDocument() on untrusted XML. v6.50.0.0 closes this residual by adding disallow-doctype-decl=true and FEATURESECUREPROCESSING=true to defaultXmlParsingConfig. Any document containing a is now rejected at parse time.

From the GitHub advisory

Summary Short summary of the problem. Make the impact and severity as clear as possible. For example: An unsafe deserialization vulnerability allows any unauthenticated user to execute arbitrary code on the server.

There is a potential XXE(XML External Entity Injection) vulnerability when http4k handling malicious XML contents within requests, which might allow attackers to read local sensitive information on server, trigger Server-side Request Forgery and even execute code under some circumstances.

Details Give all details on the vulnerability. Pointing to the incriminated source code is very helpful for the maintainer. https://github.com/http4k/http4k/blob/25696dff2d90206cc1da42f42a1a8dbcdbcdf18c/core/format/xml/src/main/kotlin/org/http4k/format/Xml.kt#L42-L46 XML contents is parsed with DocumentBuilder without security settings on or external entity enabled

PoC Complete instructions, including specific configuration details, to reproduce the vulnerability. Example Vulnerable server code:

Maven dependency:

Weakness type: CWE-200, CWE-611, CWE-918.

Product: org.http4k:http4k-format-xml (Maven) · Assigned by: GitHub_M · Published: 2024-12-12

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.91% probability of exploitation activity in the next 30 days; percentile 80.

Timeline

• 2024-12-12 — CVE record published by GitHub_M
• 2024-12-12 — GitHub-reviewed advisory GHSA-7mj5-hjjj-8rgw published (critical)
• 2026-06-09 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-7mj5-hjjj-8rgw github.com
2. CVE.org record CVE-2024-55875 cve.org
3. NVD entry CVE-2024-55875 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical Maven advisories · Today’s Security Digest