CVE-2026-61741: http4s-scala-xml has an XML External Entity (XXE) processing issue

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.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.3%, percentile 21: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 21% of all scored CVEs (low). 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.http4s:http4s-scala-xml_2.12 (Maven) <= 0.24.0, fixed in 0.24.1; org.http4s:http4s-scala-xml_2.13 (Maven) <= 0.24.0, fixed in 0.24.1; org.http4s:http4s-scala-xml_2.13 (Maven) >= 1.0.0-M1, <= 1.0.0-M38.1, fixed in 1.0.0-M39; org.http4s:http4s-scala-xml_3 (Maven) <= 0.24.0, fixed in 0.24.1. Check your lockfile, including transitive dependencies.

What it is

http4s-scala-xml provides EntityDecoder[F, scala.xml.Elem] instances that parse XML message bodies. Prior to versions 0.24.1 and 1.0.0-M39, 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. Versions 0.24.1 and 1.0.0-M39 fix the issue.

From the GitHub advisory

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.

Weakness type: CWE-611.

Product: org.http4s:http4s-scala-xml_2.12 (Maven) · Assigned by: GitHub_M · Published: 2026-09-24

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

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 none, automatable yes, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.29% probability of exploitation activity in the next 30 days; percentile 21.

Timeline

• 2026-09-24 — CVE record published by GitHub_M
• 2026-09-24 — GitHub-reviewed advisory GHSA-cjx3-73hr-rpw7 published (critical)
• 2026-09-29 — 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-cjx3-73hr-rpw7 github.com
2. CVE.org record CVE-2026-61741 cve.org
3. NVD entry CVE-2026-61741 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
4. github.com github.com

Critical Maven advisories · Today’s Security Digest