A Windows Sysmon event used to record process tampering activity, including hollowing and herpaderping. It gives defenders a telemetry signal that a process has been modified in a suspicious way, allowing the event to be forwarded to monitoring systems and correlated with broader endpoint activity.
What Sysmon Event ID 25 Means for Defenders
Sysmon Event ID 25 is a process-tampering signal, so its value is not the event name itself but the fact that Windows observed suspicious modification of a running process. That makes it a detection pivot for follow-on analysis rather than a standalone verdict.
In practice, defenders use it to decide whether a process has been hollowed, herpaderped, or otherwise manipulated in a way that may hide malicious code behind a legitimate process image. The event is most useful when it is correlated with parent-child process lineage, command-line context, image load activity, and endpoint telemetry around the same time window.
What Process Tampering Usually Indicates
Process tampering is a strong sign that an adversary is trying to make execution look normal while changing what the process actually does. Hollowing and herpaderping are both designed to separate the visible process identity from the code being executed, which can frustrate straightforward inspection.
That is why this event matters as a telemetry cue: it often appears when an attacker wants to blend into trusted Windows behavior, preserve execution under a legitimate process name, or reduce the chances that simple process listings reveal the real payload.
Because the signal is behavioral, not definitive, defenders should treat it as suspicious evidence that needs corroboration. A benign engineering or security product may also modify process behavior, so context determines whether the event represents compromise or an expected control action.
How Sysmon Event ID 25 Fits Detection Engineering
Sysmon Event ID 25 is most valuable when it is wired into broader detection logic. On its own, it says a process was tampered with; in a mature pipeline, it helps anchor alerting rules, hunt queries, and correlation with MITRE ATT&CK Enterprise techniques such as process injection, defense evasion, and credential access paths that often accompany suspicious execution.
Because it is endpoint telemetry, the event should be normalized and forwarded into central monitoring so that analysts can compare it with other host signals such as unusual network connections, unexpected child processes, and image mismatches. That correlation is what turns a single tamper event into a usable investigation thread.
Teams that rely on endpoint detections often pair this kind of telemetry with baseline hardening and detection coverage from CIS Benchmarks and control-oriented logging guidance in NIST SP 800-53 Rev 5 Security and Privacy Controls.
Why It Matters in Incident Response
When Event ID 25 appears during an investigation, it can be a lead for malware staging, post-exploitation activity, or attempted concealment of an executable’s true behavior. It is especially valuable when analysts are trying to distinguish a noisy system from a host where an attacker has already altered process memory or process content.
The event can also help narrow the time of compromise. If a tamper event precedes network beaconing, privilege escalation, or a suspicious service launch, it can become the pivot point for reconstructing the attacker’s sequence of actions.
For environments that already forward endpoint events into a detection stack, the event becomes more actionable when linked to NIST Cybersecurity Framework 2.0 detect and respond outcomes, because the operational goal is not just to record tampering but to investigate it quickly enough to contain a live compromise.
Risk and Threat Considerations
Process tampering is risky because it is often used to conceal malicious execution inside something that still looks like a normal process. That means defenders may see a legitimate image name while the actual runtime behavior has already been altered.
Failure mechanism: An attacker tampers with process content or memory so the visible process identity and the executing payload no longer match, reducing the reliability of casual inspection and slowing triage.
Impact: This can enable stealthy persistence, evade basic endpoint review, and delay containment while the modified process continues to execute or stage additional activity.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
MITRE ATT&CK addresses the attack and risk surface, while NIST CSF 2.0, NIST SP 800-53 Rev 5, CIS Controls v8 and OWASP ASVS set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| MITRE ATT&CK | T1055 — Process Injection | Process tampering commonly overlaps with ATT&CK evasion and execution techniques. |
| Recommendation — Map tamper events to ATT&CK process-manipulation techniques and hunt for related evasion activity. | ||
| NIST CSF 2.0 | DE.CM-01 — Monitoring for Anomalous Activity | Sysmon Event ID 25 is endpoint telemetry used to detect suspicious process modification. |
| Recommendation — Forward Event ID 25 into monitoring to detect anomalous process tampering. | ||
| NIST SP 800-53 Rev 5 | AU-12 — Audit Record Generation | Sysmon event logging depends on generating host audit records for suspicious process activity. |
| Recommendation — Ensure endpoint audit generation captures process tampering events for later investigation. | ||
| CIS Controls v8 | CIS-8 — Audit Log Management | This event is valuable only when logs are collected, retained, and reviewed centrally. |
| Recommendation — Centralize and review Sysmon logs so tamper events are available to analysts. | ||
| OWASP ASVS | V16 — Security Logging and Error Handling | The term is a logging and detection concept, so log quality and review discipline matter. |
| Recommendation — Preserve tamper telemetry in logs that support investigation and correlation. | ||
Practitioner Guidance
What to watch for: Treat Event ID 25 as a high-value correlation signal, not a standalone incident conclusion. Analysts should confirm whether the event lines up with other host telemetry, whether the process was expected to self-modify, and whether the surrounding execution chain makes sense for the workload.
Common misunderstanding: A process tamper event is not automatically malware, but it is rarely worth ignoring. The right response is to validate context, compare it to known-good software behavior, and decide whether the event belongs to a legitimate updater, security tool, or an active attack path.
Practitioner takeaway: The event is most useful when it is operationalized into correlation and triage workflows, because its real value comes from proving that suspicious process behavior occurred at a specific moment on a specific host.
