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Windows Graphics Component RCE Vulnerability

IdentifiersCVE-2016-3393CWE-190

CVE-2016-3393 is a vulnerability in the Windows Graphics Device Interface (GDI/GDI+) and specifically in win32k.sys, in the cjComputeGLYPHSET_MSFT_GENERAL function that parses the cmap table of a TrueType font (TTF). A specially crafted font can trigger an integer overflow during calculation of the allocation size for internal glyph/segment structures. The resulting under-allocation is followed by processing of attacker-controlled segment ranges from the font, leading to out-of-bounds memory corruption. Microsoft describes the issue as a remote code execution vulnerability reachable via a crafted web site, while Kaspersky’s analysis shows it was also used as a post-exploitation/elevation step by loading a malicious TTF from memory with AddFontMemResourceEx. Affected platforms include Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8.1, Windows Server 2012/2012 R2, Windows RT 8.1, and Windows 10 Gold/1511/1607.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can result in arbitrary code execution. In practical attack chains, the flaw was used to corrupt memory during font parsing and execute a second-stage payload with higher privileges, including escaping a browser sandbox after initial browser compromise. On affected systems this can enable full compromise of the targeted host, including execution of attacker-controlled code, installation of malware, and follow-on post-exploitation activity. On Windows 10, the same bug was reported to still be reachable in the font-processing path, though font processing occurs in a restricted user-mode process and loading the exploit font can crash fontdrvhost.exe.

Mitigation

If you can’t patch tonight, do this now.

Until patching is complete, reduce exposure to untrusted font content delivered through web browsing and document rendering paths. Limit or harden browser-based attack surface, especially where untrusted web content can trigger font parsing, and use exploit mitigation controls such as sandboxing, least privilege, and endpoint protections capable of detecting exploit behavior. Because the flaw was observed in chains that used an initial browser exploit followed by this vulnerability, reducing exposure to malicious web content and restricting post-exploitation execution paths can lower risk, but these are compensating controls rather than complete fixes.

Remediation

Patch, then assume compromise.

Apply Microsoft’s MS16-120 security update that addresses CVE-2016-3393 in the Windows graphics/font parsing components. Remediate by updating all affected Windows versions listed in the advisory to the vendor-fixed builds. Standard patch validation should include testing applications and workflows that rely on custom or embedded fonts.
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
Microsoft CorporationWindows 10 1507operating_system
Microsoft CorporationWindows 10 1511operating_system
Microsoft CorporationWindows 10 1607operating_system
Microsoft CorporationWindows 7operating_system
Microsoft CorporationWindows 8.1operating_system
Microsoft CorporationWindows Rt 8.1operating_system
Microsoft CorporationWindows Server 2008operating_system
Microsoft CorporationWindows Server 2012operating_system
Microsoft CorporationWindows Vistaoperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

2 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

2 SOURCESView more in app
What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.
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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence1

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures2

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2016-3393
NVD
nvd.nist.gov/vuln/detail/CVE-2016-3393
MITRE CWE · CWE-190
cwe.mitre.org
Patch
docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-120
US Government Resource
cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2016-3393