What should teams look for when validating whether a Tomcat deployment is exposed to CVE-2025-24813?

Teams should check the running Tomcat version, confirm whether partial PUT is enabled, verify the DefaultServlet readonly setting, and determine whether any applications rely on file based session persistence. Exposure is highest when a vulnerable version is paired with writable upload paths and applications that can deserialize attacker controlled session content.

Tomcat deployment checks that matter for CVE-2025-24813 exposure

Validation for this issue is not just a version check. A deployment can remain exposed when the vulnerable Tomcat build is reachable, file handling permits attacker-influenced writes, and session storage can be used to persist content that should never be trusted. The practical question is whether the application stack gives an attacker a path from upload or write capability to server-side execution or deserialisation impact. In practice, many security teams discover that exposure was present long before it was confirmed, because they checked the package version but not the writable surfaces and session persistence settings.

For teams assessing the blast radius, the important distinction is between a Tomcat instance that is merely installed and one that can be influenced through partial PUT, relaxed servlet settings, or application patterns that store sessions on disk. Guidance from the Apache Tomcat project on file upload, default servlet behaviour, and session management helps confirm those moving parts without relying on assumptions. The deployment should be treated as potentially exposed until each of those controls is verified in the running configuration, not just in documentation or build files.

How to validate the exposure path in a live deployment

Start with the running service, not the artefact in source control. Confirm the exact Tomcat version in the environment you are reviewing, then inspect the effective configuration that the instance is actually using. The version tells you whether the code is in scope, but the exposure path depends on whether partial PUT is enabled, whether the DefaultServlet is writable, and whether any application component persists sessions to files that could later be influenced.

From a validation standpoint, teams should ask three separate questions. First, can an attacker place content on disk through an HTTP method or upload workflow? Second, can that content reach a location that Tomcat serves or processes? Third, does the application deserialize or reload stored session content in a way that turns that write into an execution or corruption path? If any answer is uncertain, assume the environment still needs review.

Verify the version from the running container, package, or service output, not only from the release manifest.
Inspect whether partial PUT is enabled in the deployed servlet layer.
Check whether the DefaultServlet is set to read only, and whether that setting is inherited or overridden.
Identify whether any application uses file based session persistence or a similar disk backed session store.
Trace writable paths from the network edge to the Tomcat working directories and deployed web roots.

Apache Tomcat documentation is useful here because it distinguishes configuration defaults from what a deployment can actually expose when admins override those defaults. The validation breaks down when teams rely on a single control plane, because a secure build can still be unsafe if the live servlet settings, upload routes, or session store choices differ from the intended baseline.

Edge cases that change the answer

Tighter servlet restrictions often reduce operational convenience, so teams have to balance compatibility against the risk of giving web traffic a write path into server-managed files. That tradeoff matters most in legacy applications that depend on nonstandard upload handling or disk backed session features.

One common edge case is a deployment where Tomcat itself is patched, but the surrounding application still creates a dangerous condition through writable directories or custom file handling. Another is a reverse proxy or application gateway that obscures the true request path, making it harder to see whether partial PUT or related write behaviour is still reachable. A third is when the application does not use file based session persistence directly, but a framework or plugin does so indirectly. Current guidance is clear that the exposure question should be answered from the effective runtime behaviour, not from the nominal architecture alone.

For this reason, teams should treat “patched” and “safe” as different claims. A patched build can still be operationally exposed if the deployment preserves a write-to-disk path that the vulnerability can use. Conversely, an old build may be less risky than expected if the relevant write and persistence features are disabled, though that should be treated as a temporary state rather than a durable control.

Risk and Threat Considerations

The material risk is server-side compromise through an attacker-controlled file write that can be turned into execution or deserialisation impact. CVE-2025-24813 is especially concerning where writable paths and session persistence combine, because the vulnerability is not just about accepting a request, but about what the server later does with the written content.

Failure mechanism: An attacker abuses partial PUT or a similar write path to place content where Tomcat will later read or process it, then relies on permissive servlet behaviour or file-based session handling to convert that write into code execution, session corruption, or persistence of malicious state.

Impact: The affected host can move from web exposure to full application compromise, including unauthorized access to application data, corruption of sessions, and possible execution in the context of the Tomcat process.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

MITRE ATT&CK address the attack and risk surface, while CIS Controls v8 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.

Framework	Control / Reference	Relevance
MITRE ATT&CK	T1105 — Ingress Tool Transfer	Tomcat exposure can enable attacker file placement on the server.
Recommendation — Monitor and block unexpected server-side file transfer and write activity.
CIS Controls v8	6 — Access Control Management	Writable servlet paths and session stores reflect excessive access paths.
	8 — Audit Log Management	Validation depends on seeing the effective runtime behaviour of the deployment.
Recommendation — Restrict write access to Tomcat-served and session-persistence locations. Log and review servlet, upload, and session-persistence configuration changes.
NIST CSF 2.0	PR.AC — Identity Management, Authentication and Access Control	Exposure hinges on whether attacker-controlled writes are permitted into trusted paths.
	DE.CM — Security Continuous Monitoring	Teams need continuous visibility into the live configuration, not just the package version.
Recommendation — Enforce least-privilege access to writable Tomcat paths and session stores. Continuously verify live Tomcat settings, writable paths, and session storage mode.

Practitioner Guidance

What to prioritise: Validate the live request-to-disk path before you spend time on version-only triage. If the deployment has no writable route into a served or processed location, the practical risk is usually lower than in an instance with relaxed servlet settings and disk-backed sessions.

What to verify: Confirm the effective configuration at runtime, including servlet read-only behaviour, any enabled partial PUT support, and whether application code or an embedded framework relies on file based session persistence. Do not trust a single deployment manifest if the runtime is containerised, templated, or partially overridden.

What good looks like: A defensible assessment shows that the vulnerable version, if present, is paired with non-exploitable file handling and no session store path that would let attacker-controlled content survive long enough to be processed.

Practitioner takeaway: For this CVE, exposure is a configuration-and-path problem, not just a patch-level problem, so teams should validate the effective runtime write surface and persistence behaviour before declaring the instance safe.