Weakness · Medium
CWE-776: Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
What it is
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.
- Severity (our rating)
- Medium
- Likelihood of exploit
- Medium
- Introduced during
- Implementation, Operation
- Exploited in the wild
- No CVE in CISA's catalog
In more detail
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.
What an attacker can do
- DoS: Resource Consumption (Other) (Availability)
How to prevent it
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.
How to find it
- 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.)
H2 Security
Found it in your code?
We review where it appears, fix it with your team, and check it was not already used against you.
Talk to our teamT Academy
Stop writing it in the first place
Learn to build software and systems without weaknesses like this one, with practice on real hosts in your browser, every objective checked on the machine.
Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.