CVE-2026-44033: OFFIS DCMTK XML Parser DOS Vulnerability

CVE-2026-44033 Overview

CVE-2026-44033 is an uncontrolled recursion flaw [CWE-674] in the bundled XML parser of OFFIS DCMTK 3.7.0. The vulnerability resides in XMLNode::ParseXMLElement() and XMLNode::emptyTheNode() within ofstd/libsrc/ofxml.cc. An attacker can trigger stack exhaustion and a process crash by supplying a crafted XML document containing deeply nested elements. The parser is reachable through dcmencap when encapsulating a Clinical Document Architecture (CDA) document, and through any application that calls OFXMLParser::parseFile() or OFXMLParser::parseString() on untrusted input. The issue is resolved in commit d12e350e687530eb41e2b0c860aff4d8c04e5941.

Critical Impact

A single malformed XML file processed by a DCMTK-based medical imaging tool causes denial of service through stack exhaustion, disrupting DICOM processing workflows.

Affected Products

• OFFIS DCMTK 3.7.0
• Applications linking the bundled ofxml parser (ofstd/libsrc/ofxml.cc)
• dcmencap utility when encapsulating CDA documents

Discovery Timeline

• 2026-10-08 - CVE-2026-44033 published to NVD
• 2026-10-08 - Last updated in NVD database

Technical Details for CVE-2026-44033

Vulnerability Analysis

The DCMTK XML parser recursively descends into nested XML elements without enforcing a maximum recursion depth. Each nested element consumes additional stack frames in XMLNode::ParseXMLElement(). When the input contains thousands of nested elements, the call stack is exhausted and the host process crashes.

The same unbounded recursion exists in XMLNode::emptyTheNode(), which recursively frees child nodes. Even cleanup of a partially parsed deeply nested document triggers the condition. The flaw is categorized under [CWE-674] Uncontrolled Recursion.

Root Cause

Neither ParseXMLElement() nor emptyTheNode() tracked recursion depth or compared it against a bound before recursing. The bundled parser treated element nesting depth as effectively unlimited, trusting the input document structure.

Attack Vector

Exploitation requires an attacker to deliver a crafted XML document to a DCMTK-based application. Delivery paths include invoking dcmencap on an attacker-supplied CDA file, or any workflow that passes untrusted input to OFXMLParser::parseFile() or OFXMLParser::parseString(). User interaction is required to process the file. Successful exploitation produces a denial of service only; confidentiality and integrity are not affected.

/*
 *
- *  Copyright (C) 2011-2022, OFFIS e.V.
+ *  Copyright (C) 2011-2026, OFFIS e.V.
 *  All rights reserved.  See COPYRIGHT file for details.
 *
 *  This software and supporting documentation were slightly modified by

Source: DCMTK commit d12e350e

The patch introduces a new error code enforcing a maximum recursion depth:

    case eXMLErrorBase64DecodeTruncatedData:      return _CXML("Warning: Base64-string is truncated");
    case eXMLErrorBase64DecodeIllegalCharacter:   return _CXML("Error: Base64-string contains an illegal character");
    case eXMLErrorBase64DecodeBufferTooSmall:     return _CXML("Error: Base64 decode output buffer is too small");
+
+    // DCMTK: additional error codes
+    case eXMLErrorRecursionDepthExceeded:         return _CXML("Error: Maximum recursion depth exceeded in XML document");
    };
    return _CXML("Unknown");
}

Source: DCMTK commit d12e350e

Detection Methods for CVE-2026-44033

Indicators of Compromise

• Unexpected crashes of dcmencap or other DCMTK-linked binaries during XML or CDA processing.
• Core dumps showing deep call stacks in XMLNode::ParseXMLElement or XMLNode::emptyTheNode.
• XML files containing abnormally deep nesting levels (hundreds or thousands of opening tags without matching closures at shallow depth).

Detection Strategies

• Inspect inbound XML and CDA documents for nesting depth before passing them to DCMTK tools.
• Monitor process exit codes and segmentation faults from applications that invoke OFXMLParser::parseFile() or OFXMLParser::parseString().
• Correlate parser crashes with the SHA256 hash of the triggering input file for forensic analysis.

Monitoring Recommendations

• Alert on repeated abnormal terminations of DCMTK utilities within medical imaging pipelines.
• Log and review XML inputs processed by dcmencap in HL7 and DICOM integration workflows.
• Track DCMTK library versions across endpoints and workstations handling clinical imaging data.

How to Mitigate CVE-2026-44033

Immediate Actions Required

• Update DCMTK from the official repository to a build that includes commit d12e350e687530eb41e2b0c860aff4d8c04e5941.
• Audit all applications that embed the bundled ofxml parser and rebuild them against the patched source.
• Restrict dcmencap invocations to inputs sourced from authenticated, trusted systems only.

Patch Information

The fix is committed to the DCMTK upstream repository and adds the eXMLErrorRecursionDepthExceeded error code to enforce a maximum XML nesting depth. See the GitHub Commit Overview and the DCMTK Issue Tracker #1214 for upstream details.

Workarounds

• Pre-validate XML and CDA inputs with a hardened parser that enforces a nesting depth limit before passing files to DCMTK.
• Run DCMTK tools in sandboxed or containerized environments with constrained stack and CPU limits to contain crashes.
• Reject XML documents exceeding a reasonable element depth (for example, 256 levels) at the ingestion boundary.

# Example: reject XML files with excessive nesting before invoking dcmencap
max_depth=256
depth=$(grep -o '<' "$1" | wc -l)
if [ "$depth" -gt "$max_depth" ]; then
  echo "Rejected: XML nesting exceeds $max_depth" >&2
  exit 1
fi
dcmencap "$1" output.dcm