CVE-2021-20453 - Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')

Severity

82%

Complexity

39%

Confidentiality

70%

IBM WebSphere Application Server 8.0, 8.5, and 9.0 is vulnerable to a XML External Entity Injection (XXE) attack when processing XML data. A remote attacker could exploit this vulnerability to expose sensitive information or consume memory resources. IBM X-Force ID: 196648.

CVSS 3.1 Base Score 8.2. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L).

CVSS 2.0 Base Score 6.4. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (AV:N/AC:L/Au:N/C:P/I:N/A:P).

Demo Examples

Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')

CWE-776

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.


               
<data>&THIRTYTWO;</data>

Overview

First reported 3 years ago

2021-04-20 12:15:00

Last updated 3 years ago

2021-04-23 18:50:00

Affected Software

IBM WebSphere Application Server

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