CVE-2017-0261
Microsoft Office Use-After-Free Vulnerability
Description
CVE-2017-0261 is a high-severity vulnerability affecting Microsoft Office, carrying a CVSS 3.1 base score of 7.8. Classified under CWE-416 (Use After Free), this vulnerability allows an attacker to achieve remote code execution on affected systems by exploiting improper handling in the software's processing logic. This CVE has been added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2022-03-03, confirming active exploitation in the wild with a federal remediation deadline of 2022-03-24. With an EPSS score of 92.9% (99.77th percentile), the probability of exploitation activity is significantly elevated compared to other known vulnerabilities.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | office | 2010; 2013; 2016 |
Multiple CVSS Assessments
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- http://www.securityfocus.com/bid/98104(Broken Link, Third Party Advisory, VDB Entry)
- http://www.securitytracker.com/id/1038444(Broken Link, Third Party Advisory, VDB Entry)
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-0261(Patch, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2017-0261(US Government Resource)
Weakness Type
CWE-416: Use After Free
Use After Free (UAF) is a vulnerability that occurs when software continues to use a pointer after the memory it references has been freed. Once memory is freed, it may be reallocated for other purposes. If the dangling pointer is subsequently dereferenced, the program may read or write to memory now used for different data structures, leading to data corruption, information disclosure, or code execution. Use-after-free vulnerabilities are particularly prevalent in complex applications with manual memory management, including browsers, document parsers, and operating system kernels. This category of weakness is particularly relevant in the context of Microsoft Office, where the security boundary between user-supplied input and system-level processing must be carefully maintained to prevent exploitation. Understanding the underlying weakness mechanism is essential for both assessing the risk posed by CVE-2017-0261 and implementing effective countermeasures.
In the specific case of CVE-2017-0261, the use after free manifests within Microsoft Office's processing components. Use-after-free vulnerabilities are highly exploitable and consistently rank among the most dangerous software weaknesses. Attackers leverage heap manipulation techniques to control what data occupies the freed memory when the dangling pointer is dereferenced. By placing attacker-controlled objects (containing function pointers or vtables) in the freed space, code execution is achieved when the stale pointer is used. Browsers are frequent targets due to complex JavaScript/DOM interactions that create race conditions and memory management errors. UAF bugs have enabled numerous browser-based attacks, privilege escalation exploits, and malware campaigns. The remediation strategy for this weakness class involves implement strict ownership semantics and lifecycle management for allocated memory. use smart pointers (std::unique_ptr, std::shared_ptr in c++) that automatically manage memory and prevent dangling r. Organizations relying on Microsoft Office should prioritize patching this vulnerability, as the weakness class it belongs to is a well-understood and frequently targeted attack surface.
Learn more: CWE-416 — Use After Free
Impact Analysis
CVE-2017-0261 carries a CVSS 3.1 base score of 7.8 (HIGH), reflecting its significant potential for harm across multiple impact dimensions.
Confidentiality (HIGH): An attacker who successfully exploits this vulnerability gains the ability to access sensitive data stored on or processed by the affected system. This includes configuration files, credentials, cryptographic keys, and potentially proprietary or regulated data. In environments where the compromised system handles personally identifiable information (PII) or financial records, the confidentiality breach could trigger regulatory compliance violations and significant reputational damage.
Integrity (HIGH): Successful exploitation permits the attacker to modify data, install backdoors, alter system configurations, or inject malicious code. This level of integrity compromise means the attacker can manipulate the system to serve their objectives, whether that involves deploying ransomware, establishing persistent access, or pivoting to other systems within the network. The trustworthiness of the affected system is completely undermined once integrity is compromised at this level.
Availability (HIGH): The vulnerability can be leveraged to completely disrupt the availability of the affected service or device. An attacker can force a system crash, trigger a reload, or render the device inoperable, causing significant operational disruption. For critical infrastructure components like network devices or security appliances, even brief availability outages can have cascading effects across the organization.
Scope (Unchanged): The scope is Unchanged, meaning the impact of the vulnerability is limited to the affected component itself. While the consequences within that component can be severe, the exploitation does not directly extend to other systems or security domains.
With an EPSS score of 92.9% (99.77th percentile), this vulnerability ranks among the most likely to be exploited, reinforcing the urgency of immediate remediation.
Exploit Maturity
CVE-2017-0261 has confirmed active exploitation in the wild, as evidenced by its inclusion in CISA's Known Exploited Vulnerabilities catalog.
Active Exploitation: This vulnerability was added to the CISA KEV catalog on 2022-03-03, confirming that threat actors have actively exploited it in real-world attacks against organizations. The KEV listing represents a high-confidence indicator of exploitation, as CISA requires evidence of active exploitation before adding vulnerabilities to this catalog. Federal agencies were required to remediate this vulnerability by the deadline of 2022-03-24.
Ransomware Association: According to the CISA KEV catalog, this vulnerability has not been specifically linked to known ransomware campaigns at this time. However, the confirmed active exploitation means that threat actors are leveraging this vulnerability for other objectives such as espionage, data theft, or establishing persistent footholds within target networks.
Public Exploits: While specific public exploit code may not be widely cataloged in standard databases, the KEV listing confirms that exploitation is occurring in the wild. Threat actors may be using privately developed exploit tools or leveraging the vulnerability through commercial exploit frameworks.
EPSS Score: The EPSS score of 92.9% places this in the 99.77th percentile, indicating near-certain ongoing exploitation activity. This is among the highest-risk vulnerabilities tracked by EPSS.
KEV Remediation Deadline: 2022-03-24. Federal agencies under BOD 22-01 were required to remediate by this date, and all organizations are strongly encouraged to treat this deadline as a benchmark for their own patch management timelines.
Remediation
- Apply the vendor-provided security update immediately. Follow the guidance in the official security advisory: Vendor Advisory. This is the primary remediation action specified in the CISA KEV catalog: "Apply updates per vendor instructions." Ensure all affected versions are upgraded to a patched release as soon as possible.
- Verify all affected product versions are addressed. The following products and versions are known to be vulnerable: microsoft office (2010; 2013; 2016). Conduct an inventory of your environment to identify all instances of these products and ensure each one receives the appropriate update.
- Enforce the principle of least privilege on affected systems. Ensure that user accounts have only the minimum permissions necessary for their function. This limits the impact of local exploitation attempts by reducing the privileges available to an attacker.
- Implement application whitelisting and endpoint detection. Deploy endpoint detection and response (EDR) solutions to monitor for exploitation attempts. Use application whitelisting to prevent unauthorized code execution on affected systems.
- Monitor affected systems for signs of prior compromise. Before or during patching, review system and security logs for indicators of exploitation. Given the confirmed KEV listing, there is a realistic possibility that unpatched systems may have already been targeted. Conduct forensic analysis if anomalies are detected.
- Establish ongoing patch management practices for this product. Ensure Microsoft security advisories are monitored continuously. Subscribe to vendor notification channels and integrate patch testing and deployment into your organization's vulnerability management lifecycle to prevent future exposure windows.
Technical Details
CVE-2017-0261 is a high-severity vulnerability in Microsoft Office that enables arbitrary code execution through exploitation of use after free. The vulnerability exists in the way Microsoft Office handles certain locally accessible operations, where insufficient validation or improper processing of local input or system operations allows an attacker to trigger the vulnerable condition.
The attack vector is Local (AV:L), meaning the attacker requires local access to the target system. The attack complexity is low complexity (AC:L), indicating that reliable exploitation does not require specialized conditions or preparation beyond having access to the attack vector. The vulnerability requires no privileges (PR:N) and user interaction (such as opening a malicious file or visiting a crafted webpage) (UI:R).
The scope is Unchanged (S:U), indicating the impact is contained within the vulnerable component's own security scope. The combined impact ratings of HIGH/HIGH/HIGH for Confidentiality/Integrity/Availability reflect the high-severity nature of this flaw. The root cause — use after free — is a well-documented weakness class with established exploitation techniques, making this vulnerability a reliable target for attackers who have network access or the ability to deliver malicious input to the affected component. Affected products include: microsoft office (versions: 2010; 2013; 2016).
Frequently Asked Questions
Is CVE-2017-0261 actively exploited?
Yes, CVE-2017-0261 is confirmed to be actively exploited in the wild. It was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2022-03-03, which requires evidence of active exploitation before a vulnerability can be listed. While not specifically linked to ransomware campaigns at this time, the confirmed exploitation means threat actors are leveraging it for various malicious objectives. The EPSS score of 92.9% (99.77th percentile) further underscores the high likelihood of ongoing exploitation activity. Organizations should treat this as an urgent security issue requiring immediate attention.
What products are affected by CVE-2017-0261?
CVE-2017-0261 affects Microsoft Office. Specifically, the following product versions have been identified as vulnerable: microsoft office (versions: 2010; 2013; 2016). Organizations should conduct a thorough inventory of their environments to identify all deployments of the affected software. Both production systems and development or staging environments should be included in this assessment, as any unpatched instance represents a potential entry point for attackers.
How do I fix CVE-2017-0261?
Apply the security update provided by Microsoft according to their official advisory. The vendor advisory is available at: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-0261. Ensure all instances of the affected product in your environment are updated to a patched version. While deploying patches, implement compensating controls such as network access restrictions and enhanced monitoring to reduce exploitation risk. After remediation, verify that the patch was successfully applied and review system logs for any indicators of prior compromise, as unpatched systems may have been targeted before the fix was deployed.
How severe is CVE-2017-0261?
CVE-2017-0261 is rated HIGH with a CVSS 3.1 base score of 7.8. The vulnerability requires local access to exploit, with low attack complexity, and requires user interaction to trigger. The impact across confidentiality, integrity, and availability is all rated High, meaning successful exploitation can result in complete system compromise. Its inclusion in the CISA KEV catalog with a remediation deadline of 2022-03-24 confirms the real-world severity. The EPSS score of 92.9% places it in the 99.77th percentile for exploitation likelihood.
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