CVE-2015-5119 is an use-after-free vulnerability in Adobe Flash Player. CISA added it to the Known Exploited Vulnerabilities catalogue on 3 March 2022, which means attackers have used it in real attacks. A use-after-free vulnerability exists within the ActionScript 3 ByteArray class in Adobe Flash Player that allows an attacker to perform remote code execution.
What this vulnerability means in Adobe Flash Player
A use-after-free flaw means Flash can keep using memory after it has been released, which can corrupt program state and let an attacker influence execution. In this case, the weakness sits in the ActionScript 3 ByteArray class, so malicious content can target a common data-handling path rather than a niche edge case.
That matters because Flash Player processed untrusted web content at scale, and memory-unsafe bugs in browser plugins have historically been attractive for drive-by exploitation. When a bug reaches code execution, the issue is no longer just a crash risk, it becomes a foothold for running attacker-controlled code in the victim process.
Why this kind of memory corruption is dangerous
Use-after-free vulnerabilities are dangerous because they can turn object lifetime mistakes into control-flow manipulation. If an attacker can shape the contents of freed memory or influence allocations that reuse it, the program may read or write attacker-controlled data as if it were still valid.
In practice, that can lead to remote code execution, browser compromise, or a broader chain into the host system. A plugin exploit is especially concerning when it is delivered through ordinary web browsing, because users often do not need to download a separate payload or interact with a suspicious file.
For context on how this weakness class is tracked and described, the CVE Program is the canonical identifier system, while the NIST National Vulnerability Database is the standard place to review the record and related vulnerability data.
How organisations assess exposure and reduce attack surface
Exposure starts with knowing whether Flash Player still exists anywhere in the environment, including legacy desktops, VDI images, kiosk systems, browser bundles, or archived build images. For a browser plugin vulnerability, internet exposure and user reach matter as much as the software itself, because the exploit path is often remote and opportunistic.
Organisations should verify whether any externally reachable systems or legacy applications still depend on the affected component, then confirm whether vendor guidance and removal recommendations have been applied. For broader prioritisation of issues that have already been exploited in the wild, the Vulnerability Management Guide is useful for tying asset scope, KEV status, verification, and remediation tracking together.
Where a vulnerable plugin cannot be removed immediately, compensating controls should narrow who can reach the content, reduce script execution paths, and limit what the browser process can do if exploitation succeeds. The goal is to make a successful exploit less useful, not merely to document it.
Detection, incident review, and post-exploitation identity impact
Because this CVE is a remotely exploitable code execution flaw, defenders should treat suspicious browser crashes, unusual child processes, malformed content delivery, and unexpected network activity as potential compromise signals. Detection is often indirect, since exploit delivery may look like normal web traffic until the memory corruption is triggered.
After patching or removal, review the host for persistence, dropped files, unusual autoruns, and lateral movement that may have followed initial execution. If an attacker reached the endpoint, rotate credentials, tokens, keys, and any service accounts that may have been accessible from the compromised session, because exploit success can quickly become credential theft or session abuse.
Memory corruption exploits often warrant a post-incident review that is broader than the plugin itself, especially if the endpoint had access to mail, password managers, admin portals, or internal applications. The issue is not only whether the vulnerability was present, but what the attacker could do once code execution was achieved.
Risk and Threat Considerations
Because this vulnerability was added to CISA’s Known Exploited Vulnerabilities catalogue, the practical risk is not theoretical, it is that real attackers used it to gain code execution. For organisations that still had Flash-enabled browsers or legacy content flows, the main danger was untrusted web content reaching a memory-unsafe plugin before users or defenders noticed.
Failure mechanism: A use-after-free condition can let attacker-controlled data occupy memory that the program still treats as a live ByteArray object, which can destabilise execution and support code execution.
Impact: Successful exploitation can compromise the browser process, enable malware delivery, and create follow-on risks such as credential theft, persistence, and lateral movement from the affected workstation.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST SP 800-53 Rev 5, CIS Controls v8 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | SI-2 — Flaw Remediation | CVE exposure and exploited-vulnerability remediation map to flaw tracking and fix deployment. |
| SI-4 — System Monitoring | Browser exploit detection depends on monitoring for suspicious execution and compromise indicators. | |
| Recommendation — Track this CVE as a flaw-remediation priority and verify affected assets are patched or removed. Monitor endpoints for anomalous browser behaviour, crash patterns, and post-exploit activity. | ||
| CIS Controls v8 | CIS-7 — Continuous Vulnerability Management | This CVE is KEV-listed and should be governed through active vulnerability prioritisation and verification. |
| CIS-10 — Malware Defenses | Remote code execution can deliver malware, so defensive controls need to contain post-exploit payloads. | |
| Recommendation — Prioritise and validate remediation for KEV-listed software exposure across the asset estate. Apply malware defences to limit payload execution and contain suspicious files or processes. | ||
| NIST CSF 2.0 | ID.RA-01 — Asset Vulnerability Identification | Exposure assessment here starts with identifying vulnerable assets and their reachable attack surface. |
| PR.DS-01 — Data-at-Rest Is Protected | If exploitation reaches sensitive endpoints, protecting stored data and credentials reduces downstream damage. | |
| Recommendation — Identify where Flash remains in the environment and assess the reachable exposure path. Protect sensitive data and stored secrets on endpoints that may be exposed to exploitation. | ||
Practitioner Guidance
Why practitioners should care: Flash use-after-free issues are high-priority not because they are abstractly severe, but because they often enable remote exploitation through ordinary browsing. If a legacy dependency still requires Flash content, treat that dependency as a temporary exception that needs explicit ownership and deadline-based removal.
What to watch for: Look for any remaining Flash runtime presence, any application path that still launches browser-based Flash content, and any evidence that the plugin is still reachable from untrusted sources. If those conditions exist, the environment should be treated as exposed until the component is removed or isolated.
Practitioner takeaway: For an exploited memory-corruption CVE, the safest assumption is that patching alone is not enough, because you also need to check whether the endpoint was already used as an entry point.