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GHSA-cjx3-73hr-rpw7

CriticalCVSS 9.3 / 10
Published Sep 24, 2026·Last modified Sep 24, 2026
Affected Components(5)
Maven logoorg.http4s/http4s-scala-xml_2.13
1.0.0-M1 – 1.0.0-M39
Maven logoorg.http4s/http4s-scala-xml_2.13
< 0.24.1
Maven logoorg.http4s/http4s-scala-xml_3
1.0.0-M1 – 1.0.0-M39
1 / 2
Description

http4s-scala-xml provides EntityDecoder[F, scala.xml.Elem] instances that parse XML message bodies. These decoders used a javax.xml.parsers.SAXParserFactory obtained from SAXParserFactory.newInstance without any security configuration. With the JDK's default settings, the parser resolves DOCTYPE declarations, external general and parameter entities, and external DTDs.

An application that uses these decoders to parse untrusted XML is vulnerable to XML External Entity (XXE) attacks. An attacker can craft a request that:

  • discloses local files readable by the service process,
  • performs server-side request forgery (SSRF) against internal network resources, and/or
  • causes denial of service through entity expansion.

Impact

Any service that derives an XML EntityDecoder from this library and parses attacker-controlled input is affected.

Patches

The default SAXParserFactory is now hardened:

  • secure processing is enabled
  • DOCTYPE declarations are disallowed
  • external general/parameter entities and external DTD loading are disabled
  • DTD URIs are not resolved
  • XInclude is disabled.

These defaults match scala.xml.XMLLoader's defaults since 2.0.0.

Workarounds

Before upgrading, override ElemInstances#saxFactory with a hardened factory.

  val secured = new ElemInstances {
    override protected val saxFactory = {
      val f = javax.xml.parsers.SAXParserFactory.newInstance
      f.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true)
      // etc.
      f
    }
  }
  import secured._
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Risk Scores
Base Score
9.3

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a low impact on the availability of the system.

Threat Intelligence
8.5

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
0.29%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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