XXE in expat library

1) XML External Entity injection

EUVDB-ID: #VU18923

Risk: Medium

CVSSv3.1: 6.7 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:P/RL:O/RC:C]

CVE-ID: CVE-2018-20843

CWE-ID: CWE-611 - Improper Restriction of XML External Entity Reference ('XXE')

Exploit availability: Yes

Description

The vulnerability allows a remote attacker to gain access to sensitive information.

The vulnerability exists due to insufficient validation of user-supplied XML input including XML names that contain a large number of colons. A remote attacker can pass a specially crafted XML code to the affected application and view contents of arbitrary files on the system or initiate requests to external systems.

Successful exploitation of the vulnerability may allow an attacker to view contents of arbitrary file on the server or perform network scanning of internal and external infrastructure.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

expat: 1.95.0 - 2.2.6

External links

http://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5226
http://github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes
http://github.com/libexpat/libexpat/issues/186
http://github.com/libexpat/libexpat/pull/262
http://github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
http://usn.ubuntu.com/4040-1/
http://usn.ubuntu.com/4040-2/

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.