Yes. CISA added CVE-2015-5122 to its Known Exploited Vulnerabilities catalogue on 13 April 2022, which it does only when there is reliable evidence of active exploitation. CISA has not linked it to known ransomware campaigns. Use-after-free vulnerability in the DisplayObject class in the ActionScript 3 (AS3) implementation in Adobe Flash Player allows remote attackers to execute code or cause a denial-of-service (DoS).
How to confirm active exploitation without over-reading the CVE record
For a question like this, the key signal is not whether the weakness exists, but whether an authoritative source says it is being used in real attacks. CISA’s KEV catalogue is the practical confirmation point because inclusion means CISA has enough evidence to treat the issue as actively exploited. That makes the record useful for triage, but it does not by itself tell you whether your environment was targeted.
For context and authoritative recordkeeping, compare the CISA listing with the CVE Program entry and the CISA Known Exploited Vulnerabilities Catalog. Use those sources to verify the vulnerability identity, then use your own asset inventory to determine whether Flash Player is present anywhere it should not be.
One practical complication with actively exploited browser and plugin flaws is that exposure can persist after formal product end-of-life, especially where old desktops, legacy web apps, or isolated training systems still retain the software. That means the first question is often inventory, not patch status: if the software is still installed, assume the attack surface still exists until you prove otherwise.
What the exploitability means for legacy Flash exposure
A use-after-free in Flash Player is a memory-safety failure, so exploitation can move from a simple crash into code execution when an attacker can shape memory at the right time. That is why exploitation in the wild matters more than the weakness label itself: the same bug can be a nuisance in a lab and a reliable intrusion path in an exposed browser environment. The underlying security issue is trust in a plugin that can still process untrusted content.
For defenders, the most important operational distinction is between theoretical exposure and reachable exposure. If Flash is disabled in browsers but still present on endpoints, or if it remains installed for a niche application, the risk may be reduced but not eliminated. If users can reach the affected content path from a browser, the exposure is materially higher because drive-by delivery is plausible.
When a vulnerability is already in KEV, the response priority is driven by observed abuse, not by internal severity debates. In practice, that means you should treat the issue as a removal or mitigation problem first, and a hunting problem second. The Zero-Day and Exploited Vulnerabilities Guide is useful here because the same triage logic applies: confirm exposure, reduce reachability, then verify whether compromise occurred before you normalise the finding away.
What to do if patching or removal is delayed
If you cannot remove or fully disable the software immediately, reduce the chance that exploitation can occur at all. In practice, that means restricting access to the affected systems, blocking untrusted content paths where possible, and placing the legacy application behind stronger browser and network controls. The safest short-term outcome is to make the vulnerable component unreachable while you work the longer-term remediation.
For teams that still have legacy content dependencies, the decision point is whether the business function truly requires the vulnerable plugin or whether the dependency is only historical. If the latter is true, decommissioning is usually cleaner than compensating control layering, because old browser plugins are difficult to observe and easy to reintroduce accidentally.
If you are forced to keep a legacy path alive, preserve evidence of the decision: where Flash remains installed, who approved the exception, and what compensating restrictions were applied. That evidence matters if you later need to explain exposure, investigate suspicious browser activity, or justify why the exception should no longer exist.
Risk and Threat Considerations
Actively exploited browser plugin flaws are attractive because they can turn routine web usage into code execution or denial of service. The danger is highest where the vulnerable component is still reachable from ordinary user browsing, because exploitation may require little more than a visit to a crafted page or the loading of malicious content.
Failure mechanism: A use-after-free can let attacker-controlled data occupy memory that the application later trusts, which can corrupt execution flow or crash the process. In a browser-facing context, that can become a foothold for further compromise if the endpoint is poorly hardened.
Impact: The immediate effect may be remote code execution or denial of service, but the broader consequence is endpoint compromise, browser session abuse, and a larger blast radius if the affected host has access to sensitive internal resources.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
CIS Controls v8 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| CIS Controls v8 | CIS-7 — Continuous Vulnerability Management | Actively exploited CVEs require rapid identification and remediation prioritisation. |
| CIS-4 — Secure Configuration of Enterprise Assets and Software | Legacy Flash exposure often persists through insecure or unnecessary software installation. | |
| Recommendation — Prioritise and remediate KEV-listed vulnerabilities through a continuous vulnerability management process. Remove or disable obsolete software and harden endpoints so legacy plugins cannot remain reachable. | ||
| NIST CSF 2.0 | ID.RA-01 — Asset Vulnerability Identification | This question depends on confirming whether vulnerable software exists in the environment. |
| PR.DS-01 — Data-at-rest is protected | Not selected | |
| Recommendation — Identify affected assets and verify whether the vulnerable component is present and exposed. | ||
Practitioner Guidance
What to verify: Confirm whether Flash Player is still installed anywhere in the estate, whether any browser or embedded workflow can still invoke it, and whether the asset is internet-reachable. If you can only find the software on a “rarely used” machine, treat that as exposure until proven otherwise.
Decision rule: If the system is still using Flash for a live business process, prioritise removal or replacement over exception handling. If removal is impossible in the short term, isolate the host, limit user access, and treat the exception as temporary with an owner and expiry date.
What to prioritise: Check for signs of prior compromise on endpoints that could have reached Flash content, especially unusual browser crashes, suspicious child processes, or unexpected post-exploitation tooling. A KEV-listed issue justifies a fast compromise review, even if no alert was originally raised.
Practitioner takeaway: For KEV-listed browser/plugin flaws, the fastest safe path is usually to eliminate reachability first and investigate compromise in parallel, because waiting to prove abuse before acting leaves the widest attack window open.