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 in Practice
sysmon event id 25 is a high-signal endpoint telemetry event for process tampering. It tells defenders that a process image has been altered in a suspicious way, which makes it especially useful when attackers try to hide execution through techniques such as hollowing or related replacement methods.
Because the event reflects tampering after process creation, it is less about routine process activity and more about suspicious state change. That makes it valuable for distinguishing normal execution from cases where the process that appears to be running is not the process that was originally launched.
Why Process Tampering Is Security-Relevant
Process tampering matters because it is often used to blend malicious code into a legitimate process context. Attackers value that concealment because it can reduce the visibility of file-based detections, confuse analysts, and let malware inherit the trust and footprint of a benign parent process.
sysmon Event ID 25 is therefore not just another log line, it is a clue that the endpoint may be in a post-exploitation state. For defenders, it can help separate simple execution from stealthy modification, especially when correlated with process creation, image load, command-line, and memory-related telemetry.
A practical way to interpret the event is to treat it as a suspicion amplifier rather than a standalone verdict. One event may indicate investigation-worthy tampering, but the strongest conclusions usually come from correlation with adjacent endpoint telemetry and the surrounding host behaviour.
How Defenders Use the Event for Detection
In most environments, Event ID 25 becomes useful when it is forwarded into a SIEM or EDR pipeline and joined to other process and memory signals. It works best when teams can compare the tampered process against expected image hashes, parent-child relationships, signed binaries, and the command line that launched the process.
The event is also most valuable when organisations already maintain a baseline for high-risk endpoints, such as administrator workstations, servers with sensitive roles, or systems that commonly attract hands-on-keyboard activity. Those baselines make tampering stand out faster and reduce the chance that the alert is buried among noisier endpoint events.
When used well, the event helps security teams ask a sharper question: was this a legitimate process that later changed, or a malicious process that used a legitimate shell as cover? That distinction often determines whether the response focuses on tuning, containment, or full compromise investigation.
Response and Investigation Priorities
When Event ID 25 appears, the immediate goal is to establish scope, not just confirm the tamper event itself. Defenders should review the affected host for related process activity, recent logons, suspicious child processes, abnormal network connections, and any evidence that the process was used as part of a larger intrusion chain.
Post-patch or post-remediation review matters too, because tampering often means an attacker already had execution on the system. Teams should check whether any credentials, tokens, or service context used by the process may have been exposed, and whether the host continued to run attacker-controlled payloads after the tamper event.
For environments that rely heavily on endpoint telemetry, the most important question is whether the detection was isolated or part of a repeatable pattern. Repeated tampering across multiple hosts usually points to a broader intrusion campaign or a living-off-the-land technique that deserves wider hunt coverage.
Risk and Threat Considerations
Process tampering is dangerous because it can hide malicious code inside a process that defenders expect to trust. That creates a visibility gap, especially when the tampered process is used to stage additional payloads, evade simple allowlists, or mask follow-on actions from analysts.
Failure mechanism: A benign-looking process is started and then altered in memory or execution state, allowing hostile code to run under a misleading process identity and reducing the chance of straightforward detection.
Impact: The attacker gains stealth, can extend persistence or lateral movement, and may force defenders to investigate an incident only after the endpoint has already been used for broader compromise 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, CIS Controls v8, NIST SP 800-53 Rev 5 and OWASP ASVS set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| MITRE ATT&CK | T1055 — Process Injection | Sysmon Event ID 25 commonly surfaces process tampering used in ATT&CK process injection tradecraft. |
| Recommendation — Map tamper events to T1055 techniques and hunt for injected or hollowed process activity. | ||
| NIST CSF 2.0 | DE.CM-01 — Continuous Monitoring | Event ID 25 is endpoint telemetry that supports continuous monitoring and detection coverage. |
| Recommendation — Forward Sysmon tamper events into continuous monitoring so suspicious process changes are investigated quickly. | ||
| CIS Controls v8 | CIS-8 — Audit Log Management | Sysmon Event ID 25 depends on logging, collection and retention of endpoint audit data. |
| Recommendation — Centralise and retain Sysmon logs so process tampering events remain available for alerting and review. | ||
| NIST SP 800-53 Rev 5 | AU-6 — Audit Record Review, Analysis, and Reporting | Tamper telemetry needs review and correlation to become actionable incident evidence. |
| Recommendation — Review and correlate Event ID 25 with other audit records to determine whether compromise occurred. | ||
| OWASP ASVS | V16 — Security Logging and Error Handling | The term is fundamentally about security logging that preserves detection signals for suspicious execution changes. |
| Recommendation — Validate that logging and alerting preserve tamper evidence needed for investigation. | ||
Practitioner Guidance
What to watch for: Treat Event ID 25 as a trigger to enrich the alert with process lineage, command-line context, image provenance, and any correlated endpoint telemetry that can confirm or refute tampering. It is most useful when analysts do not stop at the event itself.
Governance implication: Teams should define who owns Sysmon tuning, forwarding, retention, and triage for this event class so that tamper signals do not get lost in generic endpoint noise. Sysmon Guide is a useful reference for event IDs, filtering, tamper detection and SIEM forwarding, while Endpoint Telemetry Guide helps place Sysmon in a broader detection stack.
Practitioner note: If your environment already tracks process injection, hollowing or fileless tradecraft, T1055 Process Injection Defensive Guide provides a natural next step for understanding how tampering fits into attacker behaviour and detection strategy.
Related resources from NHI Mgmt Group
Deepen Your Knowledge
Free weekly newsletter
Subscribe to the NHI & AI Identity Journal
The latest on NHI and Agentic AI security – articles, research, breaches, news and events every week.
Bonus 33% off our NHI Course when you subscribe.
Reviewed and updated by the NHIMG editorial team on October 30, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org