Published : May 1, 2026, 9:16 p.m. | 3 hours, 4 minutes ago
Description :Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion when WebSocket permessage-deflate compression is enabled.
‘Elixir.Bandit.WebSocket.PerMessageDeflate’:inflate/2 in lib/bandit/websocket/permessage_deflate.ex calls :zlib.inflate/2 with no output-size cap, then materializes the entire decompressed payload as a single binary via IO.iodata_to_binary/1. The websocket_options.max_frame_size option only bounds the on-the-wire (compressed) frame size, not the decompressed output. A high-ratio compressed frame (e.g. uniform data at ~1024:1 ratio) can stay well under any wire-size limit while forcing GiB-scale heap allocations in the connection process before any application code runs.
An unauthenticated attacker who can open a WebSocket connection can send a single such frame to exhaust the BEAM node’s memory and trigger an OOM kill.
This vulnerability requires both Bandit’s server-level websocket_options.compress and the per-upgrade compress: true option passed to WebSockAdapter.upgrade/4 to be enabled. Stock Phoenix and LiveView applications are not affected as they default to compress: false.
This issue affects bandit: from 0.5.9 before 1.11.0.
Severity: 8.2 | HIGH
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Google Gemini (gemini-2.5-flash) • CVE: CVE-2026-39804
N/A
Based on the CVE ID and the lack of specific NVD data, this remediation guide assumes a critical vulnerability in a widely used software component or application that could lead to remote code execution, unauthorized access, or significant data compromise. Specific details will be provided by the vendor upon official disclosure.
1. IMMEDIATE ACTIONS
Upon notification or discovery of CVE-2026-39804, organizations must undertake immediate containment and assessment actions to minimize potential impact.
1.1 Isolate Affected Systems: Identify and logically or physically isolate systems confirmed or suspected to be vulnerable. This may involve moving them to a quarantine network segment, blocking ingress/egress traffic at the firewall, or temporarily shutting down non-essential services. Prioritize internet-facing or mission-critical systems.
1.2 Review Logs for Exploitation Attempts: Immediately review system logs (e.g., web server access logs, application logs, security event logs, firewall logs, IDS/IPS alerts) for any indicators of compromise (IoCs) related to the vulnerability. Look for unusual requests, unexpected process executions, unauthorized file modifications, or suspicious outbound connections.
1.3 Implement Emergency Firewall Rules: If specific attack patterns or source IPs are identified, implement temporary firewall rules to block known malicious traffic or restrict access to vulnerable services to only trusted internal networks.
1.4 Notify Stakeholders: Inform relevant internal teams (e.g., incident response, IT operations, legal, communications) and external parties (e.g., customers, partners, regulators) as per your organization's incident response plan.
1.5 Backup Critical Data: Perform immediate backups of critical data on potentially affected systems before any remediation steps that might alter system state.
1.6 Disable Non-Essential Functionality: If the vulnerability is tied to a specific feature or module, disable that functionality if feasible without severely impacting business operations.
2. PATCH AND UPDATE INFORMATION
As CVE-2026-39804 is a future-dated CVE with no public NVD data, specific patch information is not yet available. Organizations must actively monitor vendor advisories.
2.1 Monitor Vendor Advisories: Regularly check official vendor security advisories, mailing lists, and support portals for the software or component affected by CVE-2026-39804. The vendor will release official patches, updated versions, or specific configuration changes.
2.2 Plan Patch Deployment: Once a patch is released, develop a comprehensive plan for its deployment. This should include:
a. Testing: Apply patches in a non-production environment (staging, development, QA) to ensure compatibility and prevent service disruption.
b. Phased Rollout: Consider a phased rollout approach, starting with a small group of non-critical systems before deploying to production and critical infrastructure.
c. Rollback Plan: Have a documented rollback plan in case issues arise during or after patching.
2.3 Verify Patch Application: After applying the patch, verify its successful installation and functionality. This may involve checking software versions, reviewing installation logs, or performing basic system health checks.
2.4 Update Related Components: If the vulnerability affects a library or dependency, ensure that all applications utilizing that dependency are also updated or recompiled with the patched version.
3. MITIGATION STRATEGIES
If immediate patching is not possible or the vendor has not yet released a patch, implement the following mitigation strategies to reduce the attack surface and potential impact.
3.1 Network Segmentation: Implement or strengthen network segmentation to isolate vulnerable systems. Restrict network access to only necessary services and ports, limiting lateral movement for attackers.
3.2 Least Privilege Access: Enforce the principle of least privilege for user accounts and service accounts interacting with or running on vulnerable systems. Reduce unnecessary permissions.
3.3 Web Application Firewall (WAF) Rules: If the vulnerability affects a web application, deploy or update WAF rules to detect and block known attack patterns associated with the vulnerability. This may involve specific regex rules for HTTP request bodies, headers, or URL parameters.
3.4 Disabling Vulnerable Features: If the vulnerability is tied to a specific, non-essential feature or module of the software, disable it until a patch is available. Consult vendor documentation for safe disabling procedures.
3.5 Input Validation and Output Encoding: Ensure robust input validation is in place for all user-supplied data to prevent injection attacks. Apply proper output encoding to prevent cross-site scripting (XSS) if the vulnerability is client-side exploitable.
3.6 Endpoint Detection and Response (EDR) Rules: Configure EDR solutions to monitor for suspicious process creation, file modifications, network connections, or privilege escalation attempts that might indicate exploitation.
3.7 Reverse Proxy/API Gateway Protection: Utilize reverse proxies or API gateways to filter and inspect incoming requests, applying rate limiting and blocking known malicious payloads before they reach the vulnerable application.
4. DETECTION METHODS
Proactive detection is crucial to identify exploitation attempts or successful compromises related to CVE-2026-39804.
4.1 Log Analysis and SIEM Integration:
a. Centralize logs from all potentially affected systems (web servers, application servers, operating systems, firewalls, IDS/IPS) into a Security Information and Event Management (SIEM) system.
b. Create custom correlation rules within the SIEM to alert on specific IoCs, unusual login attempts, unexpected process executions, or large data transfers from vulnerable systems.
c. Monitor for HTTP requests with unusual payloads, unexpected user-agent strings, or malformed parameters if the vulnerability is web-based.
4.2 Intrusion Detection/Prevention Systems (IDS/IPS):
a. Ensure IDS/IPS signatures are up-to-date.
b. Monitor IDS/IPS alerts for patterns indicative of CVE-2026-39804 exploitation.