CVE-2019-1429
Microsoft Internet Explorer Scripting Engine Memory Corruption Vulnerability
Description
CVE-2019-1429 is a high-severity scripting engine memory corruption vulnerability in Microsoft Internet Explorer. The flaw exists in the way the scripting engine handles objects in memory, enabling an attacker to execute arbitrary code in the context of the current user. This Internet Explorer vulnerability combines use-after-free and out-of-bounds write weaknesses, making it particularly dangerous for exploitation. CISA has confirmed active exploitation of CVE-2019-1429 in the wild and included it in the Known Exploited Vulnerabilities catalog. With an EPSS score of 83.04% (99.2nd percentile), this vulnerability represents a high-priority threat to organizations running Internet Explorer 9, 10, or 11.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | internet explorer | 9; 10; 11 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- http://packetstormsecurity.com/files/155433/Microsoft-Internet-Explorer-Use-After-Free.html(Exploit, Third Party Advisory, VDB Entry)
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1429(Patch, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-1429(US Government Resource)
Weakness Type
CWE-416: Use After Free
The scripting engine in Microsoft Internet Explorer exhibits a use-after-free condition when handling objects in memory. Use After Free (UAF) vulnerabilities occur when software continues to use a pointer after the memory it references has been freed, allowing the dangling pointer to reference attacker-controlled data placed in the reallocated memory region. In Internet Explorer, this can be triggered through crafted JavaScript that manipulates the object lifecycle during script execution.
Learn more: CWE-416 — Use After Free
CWE-787: Out-of-bounds Write
In addition to the use-after-free condition, CVE-2019-1429 involves an out-of-bounds write vulnerability in the scripting engine. Out-of-bounds write flaws allow data to be written beyond the intended boundaries of a memory buffer, corrupting adjacent data structures and potentially enabling code execution. The combination of both weakness types in the scripting engine amplifies the exploitability and impact of this vulnerability.
Learn more: CWE-787 — Out-of-bounds Write
Impact Analysis
CVE-2019-1429 carries a CVSS 3.1 score of 7.5 (HIGH), indicating a significant security risk. The vulnerability is remotely exploitable over the network, though it requires high attack complexity and user interaction — typically requiring the victim to navigate to a malicious web page. Confidentiality (High): Successful exploitation can fully compromise the confidentiality of user data, including credentials, session tokens, and documents accessible to the current user. Integrity (High): An attacker can modify, delete, or plant data on the target system, install persistent backdoors, or alter browser configurations. Availability (High): The vulnerability can be leveraged to crash the browser process or deploy payloads that disrupt system operations. The EPSS score of 83.04% indicates highly probable exploitation activity. The dual nature of this vulnerability — combining use-after-free and out-of-bounds write weaknesses — provides attackers with multiple exploitation primitives, increasing the reliability and versatility of attack techniques.
Exploit Maturity
CVE-2019-1429 has a well-developed exploit landscape. Public exploit code is available via Packet Storm Security, providing a detailed proof-of-concept targeting the use-after-free condition in Internet Explorer. CISA has confirmed active exploitation in the wild through the Known Exploited Vulnerabilities catalog, with a remediation deadline of 2022-01-10. The EPSS score of 83.04% (99.2nd percentile) indicates highly probable exploitation activity, placing this among the most actively targeted Internet Explorer vulnerabilities. The availability of public exploit code combined with the dual weakness types (CWE-416 and CWE-787) makes this vulnerability particularly attractive to attackers, as it offers multiple exploitation paths for achieving reliable code execution.
Remediation
- Apply vendor patches immediately as mandated by CISA KEV: Apply updates per vendor instructions. Microsoft has released cumulative security updates addressing CVE-2019-1429 through the MSRC advisory.
- Update all affected Internet Explorer instances — versions 9, 10, and 11 are vulnerable. Verify that the November 2019 cumulative security update or a later update has been applied across all endpoints running Internet Explorer.
- Migrate to a modern, supported browser such as Microsoft Edge. Internet Explorer has reached end of life and no longer receives security updates, making continued use a persistent security risk.
- Restrict scripting engine capabilities through Group Policy by disabling Active Scripting in the Internet Zone and Restricted Sites zone. Implement application whitelisting to prevent unauthorized script execution and block access to untrusted websites that could deliver exploit payloads.
- Monitor for indicators of compromise including unexpected use-after-free patterns in crash dumps, unusual child process creation from iexplore.exe, and anomalous memory allocation behavior. Conduct threat hunting focused on Internet Explorer exploitation patterns and review EDR telemetry for signs of pre-patch compromise.
Technical Details
CVE-2019-1429 is a memory corruption vulnerability in the scripting engine of Microsoft Internet Explorer, classified under both CWE-416 (Use After Free) and CWE-787 (Out-of-bounds Write). The use-after-free component occurs when the scripting engine continues to reference an object after its memory has been freed during garbage collection, creating a dangling pointer that can be exploited through heap manipulation. The out-of-bounds write component involves the scripting engine writing data beyond allocated buffer boundaries during object processing. The CVSS vector (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H) reflects a network-based attack requiring no authentication but needing user interaction and high attack complexity. These two vulnerability types are complementary — the use-after-free provides a corruption primitive that can be combined with the out-of-bounds write to achieve controlled memory manipulation, enabling an attacker to construct a reliable exploitation chain that redirects execution to arbitrary code within the context of the current user process.
Frequently Asked Questions
Is CVE-2019-1429 being actively exploited?
Yes. CVE-2019-1429 is listed in the CISA Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. Public exploit code is available through Packet Storm Security. The EPSS score of 83.04% (99.2nd percentile) further confirms highly probable exploitation activity.
What products are affected by CVE-2019-1429?
CVE-2019-1429 affects Microsoft Internet Explorer versions 9, 10, and 11. The vulnerability is in the core scripting engine that handles JavaScript execution. All Windows systems running these Internet Explorer versions are at risk.
How do I fix CVE-2019-1429?
Apply the cumulative security updates from Microsoft as referenced in the MSRC advisory. All Internet Explorer 9, 10, and 11 installations must be updated. The recommended long-term fix is to migrate to Microsoft Edge or another modern browser, as Internet Explorer has reached end of life.
How severe is CVE-2019-1429?
CVE-2019-1429 has a CVSS 3.1 score of 7.5 (HIGH). The vulnerability combines use-after-free and out-of-bounds write weaknesses, providing attackers with multiple exploitation paths. With confirmed active exploitation and an EPSS score of 83.04%, this vulnerability requires immediate remediation action.
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