NULL pointer dereference in OpenSSL

1) NULL pointer dereference

EUVDB-ID: #VU48896

Risk: Medium

CVSSv3.1: 5.9 [CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H/E:P/RL:O/RC:C]

CVE-ID: CVE-2020-1971

CWE-ID: CWE-476 - NULL Pointer Dereference

Exploit availability: Yes

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a NULL pointer dereference error. A remote attacker can trigger denial of service conditions via the API functions TS_RESP_verify_response and TS_RESP_verify_token). If an attacker can control both items being compared then that attacker could trigger a crash. For example if the attacker can trick a client or server into checking a malicious certificate against a malicious CRL then this may occur. Note that some applications automatically download CRLs based on a URL embedded in a certificate. This checking happens prior to the signatures on the certificate and CRL being verified. OpenSSL's s_server, s_client and verify tools have support for the "-crl_download" option which implements automatic CRL downloading and this attack has been demonstrated to work against those tools. Note that an unrelated bug means that affected versions of OpenSSL cannot parse or construct correct encodings of EDIPARTYNAME. However it is possible to construct a malformed EDIPARTYNAME that OpenSSL's parser will accept and hence trigger this attack.

Mitigation

Update to version 1.1.1a.

Vulnerable software versions

OpenSSL: 1.0 - 1.1.1i

External links

http://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff;h=2154ab83e14ede338d2ede9bbe5cdfce5d5a6c9e
http://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff;h=f960d81215ebf3f65e03d4d5d857fb9b666d6920
http://www.debian.org/security/2020/dsa-4807
http://www.openssl.org/news/secadv/20201208.txt

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.