Security teams should patch to a fixed Tomcat release as the primary response, then reduce exposure by disabling partial PUT requests, keeping DefaultServlet read-only, and avoiding sensitive files under public upload paths. The vulnerability is most dangerous when file based session storage is enabled, so reviewing that configuration is a critical part of containment and remediation.
Containment choices that matter before the Tomcat fix lands
When a Tomcat flaw can turn an ordinary web exposure into file write activity or session tampering, the interim question is not only whether the CVE is exploitable, but which request paths and storage features actually expand the blast radius. The practical goal is to shrink the attack surface faster than the patch rollout can complete, especially on systems that accept uploads, expose writable directories, or use session mechanisms that persist to disk. For a broader control perspective on hardening and monitoring, teams can compare their containment plan with NIST SP 800-53 Rev 5 Security and Privacy Controls. In practice, many security teams only discover the risky configuration after they have already inherited it from a deployment template or a legacy application.
Which Tomcat settings and paths are the real exposure points?
Tomcat exposure is reduced most effectively by removing the conditions that make unauthorised file handling useful to an attacker. Disabling partial PUT requests closes one route that can otherwise be abused to alter files in ways the application did not intend. Keeping DefaultServlet read-only prevents the servlet container from becoming a write-capable file surface. Just as important, public upload locations should never overlap with sensitive application content, because any directory that accepts user-controlled writes can become a staging area for code, configuration, or session artefacts if the surrounding permissions are loose.
File based session storage deserves special attention because it changes a web request issue into a persistence problem. If session state is written where the web tier can later read or influence it, the impact of a write primitive becomes much larger than a single malformed request. Teams should verify not only whether the setting exists, but whether it is actively used by any application profile, clustered deployment, or container image inherited from an older baseline.
- Disable partial PUT unless a documented application need depends on it.
- Keep DefaultServlet read-only wherever the application does not require write behaviour.
- Separate upload locations from any directory that contains executable content or sensitive files.
- Check for file based session storage and treat it as a containment priority if it is enabled.
These steps are effective only while the vulnerable Tomcat instance remains exposed through a reachable web path; they do not substitute for the fixed release.
When temporary hardening is enough, and when it is not
Tighter interim hardening often reduces exploitation opportunity quickly, but it also increases operational overhead because application owners may depend on behaviours that were never meant to be public. That tradeoff matters most in mixed estates where one Tomcat instance hosts several apps with different assumptions about uploads, static content, and session persistence. Guidance here is consensus-driven: teams generally agree that shrinking write surfaces is worth the temporary friction, but they do not always agree on whether to disable a feature globally or only on the affected service.
Where this advice breaks down is in environments that cannot verify the full request path, the deployed configuration, or the application’s use of disk-backed session data. In those cases, teams should treat the interim controls as risk reduction, not exposure elimination, and accelerate patch verification rather than relying on configuration alone.
Risk and Threat Considerations
CVE-2025-24813 is dangerous because the exposed surface is not just the Tomcat runtime itself, but the combination of request handling, writable paths, and any feature that stores attacker-influenced content on disk. That creates a pathway for unauthorised file creation or modification, which can turn a web-facing issue into persistence, tampering, or code execution depending on surrounding permissions.
Failure mechanism: The risk materialises when a vulnerable Tomcat instance accepts requests that can influence files or session artefacts and the surrounding configuration leaves those artefacts reachable or reusable. If partial PUT, write-capable servlet behaviour, and file-based session storage are present together, the control boundary becomes weak enough for an attacker to place or alter content that the application later trusts.
Impact: The likely consequences are web shell placement, session manipulation, altered application behaviour, or exposure of sensitive files under public paths. In the worst case, a single exposed Tomcat node becomes a foothold for broader compromise of the hosted application environment.
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 | Tomcat exposure reduction is a vuln containment and remediation task. |
| CIS 4 — Secure Configuration of Enterprise Assets and Software | Disabling risky Tomcat features is secure configuration hardening. | |
| CIS 16 — Application Software Security | The issue involves application-layer behaviour and unsafe file handling paths. | |
| Recommendation — Prioritise rapid remediation and track exposed Tomcat assets until fixed versions are deployed. Harden Tomcat defaults by disabling partial PUT and keeping writable surfaces read-only. Review application upload and session-storage paths for unsafe file interaction. | ||
| NIST CSF 2.0 | PR.IP-1 — Baseline Configuration | Containment depends on enforcing a safer Tomcat baseline before patch completion. |
| PR.AC-4 — Access Permissions and Authorizations | Read/write exposure in Tomcat is controlled by permission boundaries. | |
| Recommendation — Apply a hardened Tomcat baseline and verify it is active across all deployed instances. Restrict write-capable paths and authorizations that let web requests alter files. | ||
Practitioner Guidance
What to prioritise: First verify whether the vulnerable instance is internet-facing, then confirm whether partial PUT and file-based session storage are enabled on any live workload. Those two checks tell teams whether the issue is merely present or operationally exploitable.
What to verify: Validate the effective runtime configuration, not just the intended deployment baseline. Security teams should check the active Tomcat settings, inherited container images, and application-specific overrides before trusting that a hardening change has actually removed exposure.
Escalation / exception: Escalate immediately if the Tomcat host accepts uploads, serves mixed static and dynamic content, or stores session data on disk in a directory that could be influenced indirectly by web traffic. Those conditions mean containment depends on more than a simple feature toggle.
Practitioner takeaway: The best interim reduction is to remove every configuration choice that turns a web request into writable or reusable disk state, because that is what turns a patchable bug into an active exposure.
Related resources from NHI Mgmt Group
- How should security teams reduce the risk of code injection in self-hosted Git services before patching is complete?
- How should security teams reduce data exfiltration risk before a full DSPM programme is complete?
- How should product security teams reduce exposure before AI reaches production?
- How should security teams reduce data exposure before connecting enterprise data to AI tools and agents?
Deepen Your Knowledge
Reviewed and updated by the NHIMG editorial team on September 10, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
