Project c-ares Security Advisory, August 10, 2021 - Permalink
Missing input validation of host names returned by Domain Name Servers in the c-ares library can lead to output of wrong hostnames (leading to Domain Hijacking).
The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2021-3672 to this issue.
An example domain which has a cname including a zero byte:
``` $ adig cnamezero.test2.xdi-attack.net
Answers: cnamezero.test2.xdi-attack.net. 0 CNAME victim.test2.xdi-attack.net\000.test2.xdi-attack.net. victim.test2.xdi-attack.net\000.test2.xdi-attack.net. 0 A 184.108.40.206 ```
When resolved via a vulnerable implementation, the CNAME alias and name of the
A record will seem to be
victim.test2.xdi-attack.net instead of
victim.test2.xdi-attack.net\000.test2.xdi-attack.net, a totally different
This is a clear error in zero-byte handling and can potentially lead to DNS-cache injections in case an application implements a cache based on the library.
This flaw exists in the following c-ares versions.
In version 1.17.2, the function has been corrected and a test case have been added to verify.
A patch for CVE-2021-3672 is available.
We suggest you take one of the following actions immediately, in order of preference:
A - Upgrade c-ares to version 1.17.2
B - Apply the patch to your version and rebuild
It was reported to the c-ares project on June 11, 2021 by Philipp Jeitner and Haya Shulman, Fraunhofer SIT.
c-ares 1.17.2 was released on August 10 2021, coordinated with the publication of this advisory.
Thanks to Philipp Jeitner and Haya Shulman, Fraunhofer SIT for the report.