The product uses XML documents and allows their structure to be defined with a Document Type Definition (DTD), but it does not properly control the number of recursive definitions of entities.
If the DTD contains a large number of nested or recursive entities, this can lead to explosive growth of data when parsed, causing a denial of service.

Primary

XEE
XEE is the acronym commonly used for XML Entity Expansion.

Billion Laughs Attack

XML Bomb
While the "XML Bomb" term was used in the early years of knowledge of this issue, the XEE term seems to be more commonly used.

Implementation

Operation

Medium

Availability
DoS: Resource Consumption (Other)
If parsed, recursive entity references allow the attacker to expand data exponentially, quickly consuming all system resources.

Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
High

Operation
If possible, prohibit the use of DTDs or use an XML parser that limits the expansion of recursive DTD entities.

Implementation
Before parsing XML files with associated DTDs, scan for recursive entity declarations and do not continue parsing potentially explosive content.

The DTD and the very brief XML below illustrate what is meant by an XML bomb. The ZERO entity contains one character, the letter A. The choice of entity name ZERO is being used to indicate length equivalent to that exponent on two, that is, the length of ZERO is 2^0. Similarly, ONE refers to ZERO twice, therefore the XML parser will expand ONE to a length of 2, or 2^1. Ultimately, we reach entity THIRTYTWO, which will expand to 2^32 characters in length, or 4 GB, probably consuming far more data than expected.

<?xml version="1.0"?><!DOCTYPE MaliciousDTD [<!ENTITY ZERO "A"><!ENTITY ONE "&ZERO;&ZERO;"><!ENTITY TWO "&ONE;&ONE;">...<!ENTITY THIRTYTWO "&THIRTYONE;&THIRTYONE;">]><data>&THIRTYTWO;</data>

CVE-2008-3281
XEE in XML-parsing library.
https://www.cve.org/CVERecord?id=CVE-2008-3281

CVE-2011-3288
XML bomb / XEE in enterprise communication product.
https://www.cve.org/CVERecord?id=CVE-2011-3288

CVE-2011-1755
"Billion laughs" attack in XMPP server daemon.
https://www.cve.org/CVERecord?id=CVE-2011-1755

CVE-2009-1955
XML bomb in web server module
https://www.cve.org/CVERecord?id=CVE-2009-1955

CVE-2003-1564
Parsing library allows XML bomb
https://www.cve.org/CVERecord?id=CVE-2003-1564

44
XML Entity Expansion

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

CWE Content Team
MITRE
2009-06-30
1.5
2009-07-27

CWE Content Team
MITRE
2010-02-16
updated Taxonomy_Mappings

CWE Content Team
MITRE
2010-12-13
updated Relationships

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Demonstrative_Examples

CWE Content Team
MITRE
2013-02-21
updated Alternate_Terms, Applicable_Platforms, Description, Name, Observed_Examples, References, Relationships

CWE Content Team
MITRE
2017-11-08
updated Likelihood_of_Exploit, References

CWE Content Team
MITRE
2018-03-27
updated Relationships

CWE Content Team
MITRE
2019-06-20
updated Relationships, Type

CWE Content Team
MITRE
2020-02-24
updated Applicable_Platforms, Relationships

CWE Content Team
MITRE
2021-10-28
updated Relationships

CWE Content Team
MITRE
2022-04-28
updated Related_Attack_Patterns

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, References, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Relationships, Weakness_Ordinalities

Unrestricted Recursive Entity References in DTDs ('XML Bomb')