CVE-2023-21716: A Critical Heap Corruption Vulnerability in Microsoft Word

CVE-2023-21716 (NVD), a critical flaw in Microsoft Office Word’s RTF parser, has been a focal point in the cybersecurity community since its private disclosure to Microsoft in November 2022. Microsoft issued a patch in their February 14, 2023, Patch Tuesday updates to address this vulnerability source.

The Vulnerability Explained

CVE-2023-21716 is a heap corruption vulnerability that resides in a DLL named “wwlib.dll”, which Microsoft Word uses while parsing an RTF document source. This flaw allows an unauthenticated, remote attacker to embed malicious code in a specially crafted rich-text format (RTF) document. If a user opens or previews this document, it could lead to remote code execution source. The severity of this vulnerability is underscored by its CVSS score of 9.8, marking it as a critical issue source.

Proof of Concept (PoC)

Shortly after the disclosure of the vulnerability, a proof-of-concept (PoC) was released, demonstrating how an attacker could exploit the vulnerability to achieve remote code execution source. This PoC is publicly available on GitHub source.

Weaponization Likelihood

Given the critical nature of this vulnerability and the public availability of the PoC, there is a high probability that this vulnerability will be weaponized quickly source. If chained with an RCE flaw, this vulnerability could be weaponized by APT actors in ransomware and malware attacks source.

APT Groups

While there are no specific APT groups reported to have used this vulnerability at the time of writing, it’s worth noting that APT groups have previously exploited similar vulnerabilities. For instance, Iron Tiger, an advanced persistent threat (APT) group, is known for exploiting similar vulnerabilities source. Additionally, a Russia-linked APT group named Winter Vivern has been reported to exploit similar vulnerabilities source.

Similarities with Other Vulnerabilities

CVE-2023-21716 shares commonalities with past vulnerabilities such as CVE-2016–001. In both instances, a crafted RTF file was used to exploit the vulnerability source. This recurring issue with Microsoft Word’s handling of RTF files suggests a potential area for future security enhancements.

Attack Vector

The primary attack vector for this vulnerability is through a malicious RTF document. An attacker could craft such a document, embedding malicious code within it. When the document is opened or previewed in Microsoft Word, the malicious code is executed, potentially granting the attacker control over the victim’s system.

Indicators of Compromise (IOCs)

The primary IOCs for this vulnerability are the receipt and opening of unexpected or suspicious RTF documents. Users should be cautious of documents from unknown sources, and organizations should implement security measures to scan and filter incoming documents for potential threats.


Microsoft has issued a patch to address this vulnerability. Users are strongly advised to update their systems to the latest version to protect against potential attacks source. Additionally, users should exercise caution when opening documents from unknown or untrusted sources.


The discovery of CVE-2023-21716 underscores the importance of regular system updates and the potential dangers of seemingly harmless files. By maintaining vigilance and keeping systems updated, users can significantly mitigate their risk of falling victim to such vulnerabilities.