CVE-2020-1967
Description
A NULL pointer dereference flaw was found in the way OpenSSL handled certain TLS handshake messages. This flaw allows an unauthenticated attacker to cause a server application compiled with OpenSSL to crash, causing a denial of service. In some cases a malicious server could also cause a client compiled with OpenSSL to crash.
Statement
This flaw was introduced by the following OpenSSL commit: https://github.com/openssl/openssl/commit/5235ef44b93306a14d0b6c695b13c64b16e1fdec which was shipped as a part of OpenSSL-1.1.1d, therefore older versions are not affected by this flaw. OpenSSL packages shipped with Red Hat Products are NOT affected by this flaw.
The affected signature_algorithm_cert check which causes the flaw is only applied to TLS 1.3, therefore older versions of TLS are not be affected by this flaw.
Also, the vulnerable SSL_check_chain() is not called directly from libssl, but may be used by the application inside a callback (e.g., client_hello or cert callback) to verify that a candidate certificate chain will be acceptable to the client. Thus, applications that use openssl without invoking the SSL_check_chain() function are not vulnerable to this flaw.
Lastly, no Red Hat Middleware products ship the affected version of OpenSSL. However, some components, such as Netty and Wildfly, may be configured by customers to use any OpenSSL version. Customers who have configured their setups to use a vulnerable version of OpenSSL are advised to upgrade to the latest unaffected version immediately.
Mitigation
Applications compiled with OpenSSL >= 1.1.1d that either use openssl without invoking the `SSL_check_chain()` function or do not use TLS 1.3 are not vulnerable to this flaw.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | 7.5 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
Integrity,Confidentiality
Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
Acknowledgements
Red Hat would like to thank the OpenSSL project for reporting this issue. Upstream acknowledges Bernd Edlinger as the original reporter.
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