Security Advisory 2021-02-02-2 - wolfSSL heap buffer overflow in RsaPad_PSS (CVE-2020-36177)

DESCRIPTION
RsaPad_PSS in wolfcrypt/src/rsa.c in wolfSSL before 4.6.0 has an out-of-bounds write for certain relationships between key size and digest size. The issue is marked as critical with CVSS score of 9.8.

REQUIREMENTS

It’s still work in progress, there is not that much information about it available yet, but according to the very high CVSS score of 9.8 (10 is most severe) it’s likely, that this issue has RCE potential.

MITIGATIONS
You need to update the affected libwolfssl24 package you’re using with the command below.

 opkg update; opkg upgrade libwolfssl24

Then verify, that you’re running fixed version.

 opkg list-installed libwolfssl24

The above command should output following:

 libwolfssl24 - 4.6.0-stable-1 - for stable OpenWrt 19.07 release
 libwolfssl24 - 4.6.0-stable-1 - for master/snapshot

The fix is contained in the following and later versions:

• OpenWrt 19.07: 2021-02-02 (fixed by v19.07.6-11-g2044c01de8f2)

• OpenWrt master: 2021-01-01 (fixed by reboot-15389-gba40da9045f7)

AFFECTED VERSIONS
To our knowledge, OpenWrt snapshot images are affected. OpenWrt stable release versions 19.07.0 to 19.07.6 are not affected, because vulnerable libwolfssl24 package is not shipped by default in the official firmware images. Older versions of OpenWrt (e.g. OpenWrt 18.06, OpenWrt 15.05 and LEDE 17.01) are end of life and not supported any more.

CREDITS
This issue was found by libFuzzer’s address sanitizer in OSS-Fuzz project and fixed by Sean Parkinson from wolfSSL team.
*[OSS]: Open Source Software