CVE-2016-7892

What Is Adobe Flash Player?

Adobe Flash Player is the legacy browser plugin and runtime for Adobe Flash content — the platform that dominated rich web experiences for over two decades. Flash Player executed ActionScript (a JavaScript-like language) and rendered multimedia content including animation, video, and games. The Flash ActionScript virtual machine manages dozens of built-in classes for UI elements (MovieClip, Sprite, TextField, Button), media (Sound, Video, NetStream), and data (Array, Object, XML). Memory safety vulnerabilities in these built-in class implementations have been the primary source of Flash Player exploits throughout its history. Flash Player reached end-of-life on December 31, 2020, and no further patches will be issued.

Overview

CVE-2016-7892 is a use-after-free vulnerability in the TextField class of Adobe Flash Player that allows remote code execution when a user views malicious Flash content. TextField is the primary class in Flash for displaying and editing text — it is used in virtually every Flash application. The UAF vulnerability occurs when Flash's memory management frees a TextField object while a live ActionScript reference to it still exists; accessing the stale reference provides the attacker with a controlled heap read/write primitive enabling code execution. Patched in APSB16-39 (December 13, 2016). Adobe Flash Player is end-of-life; all remaining Flash installations are permanently vulnerable. CISA added CVE-2016-7892 to the KEV catalog in March 2022.

Affected Versions

Technical Details

Root Cause: TextField Class Use-After-Free

CVE-2016-7892 is a use-after-free (CWE-416) specifically in Flash's TextField built-in ActionScript class. TextField objects in Flash display and edit text — they can be dynamically created, modified, and destroyed through ActionScript. The UAF vulnerability arises from Flash's internal object lifecycle management for TextField instances:

TextField UAF mechanism:

• Flash Player manages ActionScript objects through a combination of reference counting and a garbage collector
• Under specific conditions — manipulating TextField object references, event listeners, or parent-child display list relationships in a particular sequence — Flash can free a TextField object's internal memory while ActionScript code still holds an active reference to it
• Subsequent access to the TextField object through the stale reference reads attacker-controlled memory (if the freed allocation was filled by a heap spray)
• The stale pointer provides a read/write primitive: reading a "property" of the freed TextField returns attacker-controlled data; writing a property to it modifies arbitrary memory

Exploitation chain:

1. Craft ActionScript to trigger UAF — specific TextField operations create the use-after-free condition
2. Heap spray — fill freed TextField memory with fake object structures containing controlled function pointers
3. Access stale reference — ActionScript reads/writes through the dangling pointer, accessing the spray data
4. Code execution — controlled method pointer redirects Flash execution to shellcode

December 2016 Flash Patch Context

APSB16-39 (December 13, 2016) patched 17 CVEs in Flash Player, including CVE-2016-7892. The large number of vulnerabilities in a single monthly bulletin reflects the persistent vulnerability density in Flash's codebase — December 2016 was the last major Flash patch before 2017. The 2016 calendar year saw over 100 CVEs patched in Flash Player, continuing a multi-year trend of critical vulnerability discovery.

Attack Characteristics

Discovery

CVE-2016-7892 was discovered and responsibly disclosed to Adobe by security researchers; attributed in APSB16-39 as part of Adobe's coordinated December 2016 security release.

Exploitation Context

• TextField ubiquity: The TextField class is used in virtually every non-trivial Flash application — any Flash login form, text display, or user input widget uses TextField; this makes CVE-2016-7892 exploitable against a very broad range of Flash content, not just specifically crafted attacker pages
• Exploit kit integration: Flash UAF vulnerabilities were systematically incorporated into exploit kits (Angler, Magnitude, RIG, Neutrino) for drive-by malware delivery; CVE-2016-7892's December 2016 patch date aligns with known exploit kit update cycles that rapidly adopted newly disclosed Flash vulnerabilities
• End-of-life permanent exposure: Adobe Flash Player will never receive another security patch; CVE-2016-7892 and the hundreds of other Flash vulnerabilities are permanently present in any Flash installation; the only remediation is removal
• CISA KEV (2022): Added March 25, 2022, reflecting documented exploitation in attack campaigns

Remediation

1. Remove Adobe Flash Player immediately — Flash Player is permanently end-of-life with no further patches. Use the Adobe Flash Player uninstaller or Windows Add/Remove Programs to remove it from all systems.

2. Verify Flash is blocked in browsers — confirm all browsers block Flash: Chrome, Firefox, Edge, and Safari all block Flash content by default post-EOL. Check browser plugin settings to confirm no Flash plugin is active.

3. Replace Flash-dependent applications — identify any business applications or workflows requiring Flash Player and migrate them to HTML5, modern web frameworks, or replacement applications.

4. Isolate legacy systems requiring Flash — if a legacy system cannot immediately be migrated away from Flash, isolate it from the internet and restrict its network access to minimize exposure.

5. Block .swf at web gateway — configure proxy/firewall rules to block Flash (.swf) file downloads from the internet to prevent inadvertent Flash content loading.