Apache Struts 2 Flaw Lets Hackers Crash Your Server Instantly (Urgent DoS Alert)
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Apache Struts 2 Flaw Lets Hackers Crash Your Server Instantly (Urgent DoS Alert)
Issue: Disk exhaustion Denial-of-Service (DoS) via multipart upload file leak
CVE: CVE-2025-64775 (Security Bulletin S2-068)
Risk: High — Remote attackers can exhaust disk and disrupt service availability
TL;DR — What You Must Do Today
Apache Struts has a denial-of-service vulnerability where a file leak during multipart request processing can cause uncontrolled disk usage and crash services when disk fills up. This is tracked as CVE-2025-64775 (S2-068). Official Struts announcement: Apache Struts Announcements 2025.
Fix: Upgrade to Struts 6.8.0 or Struts 7.1.1 (per NVD/Apache advisory). NVD record: NVD (related DoS file leak entry).
What’s Happening: “Instant Crash” Explained
This issue is a classic availability kill-switch: attackers send crafted or repeated multipart/form-data requests (commonly used for file uploads). Due to a file leak in multipart request processing, temporary files are not cleaned up as expected. Over time (or rapidly, depending on request size and rate), disk space is exhausted and your Struts application—or even the host—can fail.
“Instantly” doesn’t always mean a single packet. In real operations, attackers combine:
- Large multipart payloads (or many moderate ones)
- High request concurrency
- Targeting hosts with limited /tmp or container ephemeral storage
The end result is the same: disk fills, services crash, alerts fire late, and recovery becomes messy.
Who Is Vulnerable?
According to NVD and Apache Struts security guidance for the multipart file-leak DoS family, impacted ranges include Struts versions spanning legacy to current branches, and remediation is achieved by upgrading to 6.8.0 or 7.1.1. See: Apache Struts Announcements 2025 and NVD detail.
- Public internet-facing Struts endpoints handling file uploads
- Apps behind weak WAF rules (multipart not inspected or rate-limited)
- Containers/VMs with small ephemeral storage allocations
- Reverse proxies passing large bodies without limits
Impact: What Attackers Can Do
- Exhaust disk space (tmp directories, upload directories, container overlay FS)
- Crash application services (OutOfDisk conditions, IO failures, app server instability)
- Trigger cascading failures (logging stops, database writes fail, queues back up)
- Create a recovery trap (services restart into the same full-disk condition)
Patch Now: The Only Real Fix
Upgrade Struts to 6.8.0 or 7.1.1 as recommended by Apache Struts security communications. Source: Apache Struts Announcements 2025.
- Identify all Struts services and versions (SBOM, build files, runtime banners).
- Prioritize internet-facing nodes and upload endpoints first.
- Upgrade to the fixed release line (6.8.0 or 7.1.1), rebuild, redeploy.
- Confirm upload flows function; verify temp file cleanup and disk behavior under load.
- Backport fix to any pinned legacy deployment where upgrade is delayed (short-term only).
If You Cannot Patch Today: Containment Controls
If patching is blocked by change windows, you must reduce blast radius immediately. These controls do not replace upgrading.
1) Enforce Request Size Limits at the Edge
- Set maximum request body sizes on reverse proxies (Nginx/Apache/ALB).
- Reject oversized multipart uploads before they reach Struts.
2) Rate Limit Multipart Endpoints
- Apply per-IP and per-session rate limits on upload routes.
- Throttle concurrent uploads (especially anonymous routes).
3) Isolate and Cap Temporary Storage
- Mount /tmp on a separate partition with quotas.
- In containers, set strict ephemeral storage limits and alerts.
- Ensure log volume is separated from temp volume.
4) WAF Rules (Practical, Not Perfect)
- Block suspicious high-frequency multipart patterns.
- Detect unusual boundary formats and repeated upload failures.
- Consider temporarily restricting file upload functionality for public users.
Detection: How SOC Teams Can Catch This Early
- Disk usage growth rate on app hosts (especially /tmp, upload dirs)
- Spike in multipart/form-data requests and upload endpoints
- Increase in HTTP 4xx/5xx tied to uploads
- App server warnings about temp files, IO errors, or file handling failures
- Container eviction events and node disk pressure alerts
If You Are Under Attack: Rapid Response Steps
- Reduce inbound traffic: enable emergency rate limits or geo/IP blocks at the edge.
- Preserve evidence: capture proxy logs, access logs, and request metadata.
- Stop the bleeding: temporarily disable or restrict upload routes.
- Recover safely: clean temp directories, validate disk health, then restart services.
- Patch immediately after stabilization to prevent repeat hits.
Why DoS in “File Upload Logic” Keeps Returning
File upload is one of the hardest application features to secure because it combines untrusted input, large data volume, concurrency, disk IO, and complex parsing rules. Attackers exploit the part defenders rarely test: long-running, repeated, edge-case multipart behavior.
CyberDudeBivash — Emergency Struts Risk Review
We can help you rapidly identify Struts exposure, validate upload endpoints, implement safe edge limits, and accelerate patch rollout without breaking production.
Tools and services hub: https://cyberdudebivash.com/apps-products/
References (Vendor and Primary Sources)
- Apache Struts announcements (2025): https://struts.apache.org/announce-2025
- NVD (DoS file leak entry): https://nvd.nist.gov/vuln/detail/CVE-2025-66675
- Apache mailing list advisory threads: https://lists.apache.org/
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