CVE-2026-31248 — XML entity expansion denial-of-service in Docling METS GBS backend

MITRE service request: 1988723

Status: RESERVED (pending a qualifying public reference per CNA Rules §5.3).

Official CVE description

Docling’s METS GBS backend is vulnerable to XML Entity Expansion (XXE) attacks thru 2.61.0. The backend extracts and validates XML files from .tar.gz archives using etree.fromstring() without disabling entity resolution. An attacker can craft a malicious XML file with nested entity definitions (XML Bomb) and package it into a .tar.gz archive. When processed by Docling, the exponential expansion of entities during XML parsing leads to excessive resource consumption, resulting in a denial of service (DoS) condition on the system running the Docling parser.

Summary

Malicious .tar.gz archives containing METS XML with nested entities pass _validate_mets_xml() → etree.fromstring without safe parser flags, causing CPU/memory exhaustion when archivists batch-convert documents.

Affected product and versions

Product: docling-project/docling.
Affected range (coordination record): through v2.61.0.

Technical details

Surface: CLI docling ... exploit_mets.tar.gz.
Sink: etree.fromstring on extracted METS XML.
Impact: Worker DoS; may stall ingestion pipelines.
Mitigation: Pre-scan tar members; parse with hardened lxml settings.

Risk

Medium–High for automated digitization pipelines.

Remediation / workaround

Upgrade TBD; quarantine untrusted archives.