In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of colons could make the XML parser consume a high amount of RAM and CPU resources while processing (enough to be usable for denial-of-service attacks).

XML External Entity vulnerability in libexpat 2.2.0 and earlier (Expat XML Parser Library) allows attackers to put the parser in an infinite loop using a malformed external entity definition from an external DTD.

The overflow protection in Expat is removed by compilers with certain optimization settings, which allows remote attackers to cause a denial of service (crash) or possibly execute arbitrary code via crafted XML data. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-1283 and CVE-2015-2716.

The XML parser in Expat does not use sufficient entropy for hash initialization, which allows context-dependent attackers to cause a denial of service (CPU consumption) via crafted identifiers in an XML document. NOTE: this vulnerability exists because of an incomplete fix for CVE-2012-0876.

Expat, when used in a parser that has not called XML_SetHashSalt or passed it a seed of 0, makes it easier for context-dependent attackers to defeat cryptographic protection mechanisms via vectors involving use of the srand function.

Expat allows context-dependent attackers to cause a denial of service (crash) or possibly execute arbitrary code via a malformed input document, which triggers a buffer overflow.

expat 2.1.0 and earlier does not properly handle entities expansion unless an application developer uses the XML_SetEntityDeclHandler function, which allows remote attackers to cause a denial of service (resource consumption), send HTTP requests to intranet servers, or read arbitrary files via a crafted XML document, aka an XML External Entity (XXE) issue. NOTE: it could be argued that because expat already provides the ability to disable external entity expansion, the responsibility for resolving this issue lies with application developers; according to this argument, this entry should be REJECTed, and each affected application would need its own CVE.