CVE-2013-3918 is an out-of-bounds write vulnerability in Microsoft Windows. CISA added it to the Known Exploited Vulnerabilities catalogue on 6 October 2025, which means attackers have used it in real attacks. Microsoft Windows contains an out-of-bounds write vulnerability in the InformationCardSigninHelper Class ActiveX control, icardie.dll. An attacker could exploit the vulnerability by constructing a specially crafted webpage.
What the vulnerability is and why it matters
An out-of-bounds write means Windows can be made to write data outside the memory region it intended to modify. In this case, the flaw sits in an ActiveX control used by Internet Explorer-era web content, so a malicious webpage can trigger memory corruption simply by being visited.
That makes the issue especially dangerous because the attack path is remote and browser-delivered, not dependent on local access. For background on how this class of weakness fits into the broader software weakness landscape, see the CWE Top 25 Guide.
How exploitation typically works
Out-of-bounds writes are often exploitable because they can corrupt adjacent memory and destabilise control flow. In browser or plugin components, that can turn a content-rendering bug into code execution if the attacker can shape the overwritten data well enough.
Here, the exploit surface is a crafted webpage, which matters because it lowers the barrier to delivery. The victim does not need to open an attachment or install software manually, and a drive-by visit may be enough to trigger the flaw.
For a broader view of how attackers chain exposed weaknesses into real intrusions, the State of NHI & AI Agent Breach Report is useful context even though this CVE itself is a Windows memory-safety issue.
How organisations check exposure and reduce it
The first exposure question is whether any supported or unsupported Windows systems still expose the vulnerable ActiveX component to users. That usually means checking endpoint inventories, browser configurations, legacy compatibility settings, and whether the affected control is still reachable in the organisation’s environment.
Because CISA placed this CVE in the KEV catalogue, organisations should treat it as a priority item and align remediation with their patch and exception process. The authoritative references are the CVE Program for record identity and NIST National Vulnerability Database for vulnerability record details and related metadata.
If patching is delayed, compensating controls usually focus on reducing browser reachability, limiting ActiveX use, hardening web filtering, and restricting exposure of systems that still depend on legacy web components. The practical goal is to make the vulnerable path harder to reach until it can be removed.
Detection, compromise review, and post-remediation checks
Because exploitation begins with webpage content and can occur before obvious user-visible failure, detection should look for unusual browser crashes, exploit-like memory faults, and suspicious page delivery patterns around affected endpoints. Where telemetry exists, security teams should review web proxy logs, endpoint alerts, and browser crash data for signs of attempted exploitation.
After patching, organisations should not stop at version verification alone. They should confirm the vulnerable path is no longer reachable, review any endpoints that were exposed during the vulnerable window, and look for secondary compromise indicators if exploitation may already have occurred.
If the attack led to successful code execution, the follow-on review should include user sessions, browser context, and any credentials or tokens present on the affected endpoint at the time of compromise.
Risk and Threat Considerations
This CVE is dangerous because it is a remotely triggerable memory-corruption flaw in a widely deployed client component, which can turn ordinary web browsing into an initial access path. When such flaws are actively exploited, the main threat is not just a crash, but the possibility of code execution and follow-on compromise on the user endpoint.
Failure mechanism: A malicious webpage drives the vulnerable ActiveX control into writing outside its intended memory bounds, creating corruption that an attacker may use to alter execution flow or destabilise the process.
Impact: Successful exploitation can expose the endpoint to code execution, browser compromise, and downstream credential or session theft if the attacker gains a foothold on the system.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
MITRE ATT&CK addresses the attack and risk surface, while CIS Controls v8, NIST SP 800-53 Rev 5 and OWASP ASVS set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| CIS Controls v8 | CIS-7 — Continuous Vulnerability Management | Prioritizes identification and remediation of exploited software weaknesses. |
| Recommendation — Prioritize and remediate KEV-listed Windows vulnerabilities through continuous vulnerability management. | ||
| NIST SP 800-53 Rev 5 | SI-2 — Flaw Remediation | Requires timely remediation of software flaws that can be exploited remotely. |
| SI-16 — Memory Protection | Addresses controls that reduce exploitability of memory corruption weaknesses. | |
| Recommendation — Track, assess, and remediate the Windows flaw under a formal flaw-remediation process. Apply memory-protection controls and hardening to reduce exposure to out-of-bounds writes. | ||
| OWASP ASVS | V15 — Secure Coding and Architecture | Maps to memory-safety weaknesses that arise from insecure software design and implementation. |
| Recommendation — Use secure coding review to prevent memory-corruption flaws that become browser-exploitable. | ||
| MITRE ATT&CK | T1203 — Exploitation for Client Execution | Covers attacker use of client-side flaws to execute code on a victim endpoint. |
| Recommendation — Detect and hunt for client-side exploitation attempts that may use malicious webpages. | ||
Practitioner Guidance
Why practitioners should care: Treat KEV-listed browser and plugin flaws as operationally urgent, especially when the delivery vector is a webpage and the vulnerable component sits on user workstations. These issues are often missed if teams focus only on server-side patch cycles.
What to watch for: Prioritise systems where legacy browser features, compatibility modes, or ActiveX remain enabled, because those environments preserve the attack surface that modern hardened configurations try to remove.
Practitioner takeaway: If you cannot remove the exposure immediately, reduce the path to exploitation first, then verify remediation with both asset-level confirmation and post-patch compromise review.