CVE-2026-12975: Apicurio Registry XXE/SSRF via Insecure XML Parser

Technical summary

The ContentTypeUtil.isParsableXml() method instantiates a SAXParserFactory without disabling XXE (XML External Entity) protection or external entity resolution. This allows attackers to craft XML payloads containing external DTD declarations or entity definitions. When the registry processes uploaded artifacts to determine content type, the parser resolves these external references, enabling blind SSRF attacks against internal network resources or denial of service via billion laughs-style entity expansion. The vulnerability is classified as CWE-611 (Improper Restriction of XML External Entity Reference).

Business impact

An attacker with artifact upload permissions can exfiltrate data from internal systems, scan the registry's network segment, or crash the registry service. Organizations relying on Apicurio Registry for API schema management face potential data exposure and operational disruption. If the registry authenticates users via SSO or internal credentials, attackers may leverage SSRF to pivot to downstream systems. Denial of service attacks could disrupt artifact management workflows for teams dependent on schema lookups.

Affected systems

Red Hat Build of Apicurio Registry is affected. The vulnerability applies to any deployment where the registry processes user-supplied XML artifacts or detects content types via the vulnerable parser. Default configurations that permit unauthenticated artifact uploads face immediate risk; hardened deployments with strict write access control reduce exposure but remain vulnerable if any authenticated user is compromised.

Exploitability

Exploitability is straightforward: an attacker uploads a specially crafted XML document containing an external entity declaration pointing to an internal IP, service endpoint, or attacker infrastructure. The parser resolves the reference during content-type detection without user interaction required. No special privileges beyond artifact-write permission are necessary. The CVSS vector reflects this accessibility (CVSS:3.1/AV:N/AC:L/PR:L), though unauthenticated exploitability in default setups would elevate practical risk. No public exploit code or active KEV listing currently exists.

Remediation

Disable external entity resolution and external DTD processing in SAXParserFactory configuration. Apply the security manager attributes: XMLConstants.ACCESS_EXTERNAL_DTD set to empty string and XMLConstants.ACCESS_EXTERNAL_SCHEMA set to empty string. Additionally, disable entity expansion limits. Verify the fix by confirming that benign XML uploads still work while malicious payloads fail silently or with controlled exceptions. Consult Red Hat security advisories for specific patched versions and deployment guidance.

Patch guidance

Monitor Red Hat security advisories for patched versions of Apicurio Registry. When updates are released, test in a staging environment before production deployment to ensure artifact compatibility and parser behavior. If the registry is containerized, rebuild images with the patched version. For air-gapped environments, validate patch availability before committing to update schedules. Verify against vendor documentation that the patched version includes XXE mitigations.

Detection guidance

Monitor artifact upload requests for XML payloads containing DOCTYPE declarations, ENTITY definitions, or external schema/DTD references. Log and alert on any outbound DNS queries or HTTP requests initiated during artifact upload or content-type detection. Review registry logs for parsing errors or exceptions during file processing, which may indicate XXE attempts. Network-level detection: inspect egress traffic from the registry for unexpected connections to internal services or external domains during artifact operations. Implement content-type validation on the client side to reject suspicious payloads before upload.

Why prioritize this

This vulnerability scores CVSS 8.5 (HIGH) and poses immediate risk in multi-user or internet-facing deployments. The combination of network accessibility, low attack complexity, and high availability impact makes it a priority for patching. Organizations with default-auth Apicurio Registry instances or those managing sensitive schemas should treat this as urgent. The lack of KEV listing does not diminish risk; the vulnerability is conceptually simple and likely to attract researcher attention.

Risk score, explained

CVSS 8.5 reflects network-accessible attack surface (AV:N), minimal complexity (AC:L), and requirement for authenticated artifact-write privilege (PR:L). The scope change (S:C) indicates the attacker can affect resources beyond the registry itself via SSRF. Confidentiality impact (C:L) accounts for data exfiltration via blind SSRF; integrity is unaffected (I:N); availability impact is high (A:H) due to entity expansion denial of service. The score appropriately captures the threat: moderate authentication barrier, straightforward exploitation, and severe operational consequences.

Frequently asked questions