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How CVE-2026-69185 Works
Socket.IO is a real-time bidirectional communication framework widely used in web applications. The vulnerability resides in the packet parsing mechanism, specifically in how the server handles binary attachments accompanying Socket.IO packets.
Under normal operation, a Socket.IO packet can include binary attachments. The server expects a certain number of attachments based on the packet header and waits to receive all of them before processing the complete message. The flaw is the absence of proper bounds checking and resource allocation limits during this process.
An attacker can craft a malicious Socket.IO packet that declares an extremely large number of binary attachments but never sends them. The server, trusting the packet’s declaration, allocates memory buffers to hold the expected attachments and enters a waiting state. Because the attachments never arrive, the server holds these buffers indefinitely, consuming memory.
By sending a continuous stream of such crafted packets, an attacker can cause the server to accumulate an unbounded number of incomplete message buffers. This leads to a steady and uncontrolled increase in memory consumption until the server’s available RAM is exhausted. The system becomes unresponsive or crashes, resulting in a denial-of-service (DoS) condition. This attack requires no authentication and can be performed over the network. The vulnerability is classified under CWE-20 (Improper Input Validation) and CWE-754 (Improper Check for Unusual or Exceptional Conditions), with a CVSS v3.1 base score of 7.5 (High). It affects all Socket.IO versions prior to the patched releases.
DailyCVE Form:
Platform: Socket.IO
Version: <4.2.7,<3.4.5,<3.3.6
Vulnerability: Memory Exhaustion (DoS)
Severity: High (CVSS 7.5)
date: 2026-08-03
Prediction: 2026-08-03 (Released)
What Undercode Say:
The vulnerability is rooted in the `socket.io-parser` component, which accepts an unlimited number of binary attachments. The fix introduces proper validation to limit concurrent binary attachments and implements timeout behaviors to prevent indefinite buffering.
Check Socket.IO Version:
npm list socket.io
Identify Vulnerable Versions:
npm list socket.io | grep -E "socket.io@([0-9]+.[0-9]+.[0-9]+)" | while read line; do version=$(echo "$line" | grep -oE "[0-9]+.[0-9]+.[0-9]+") if [[ "$version" < "3.3.6" ]] || \ [[ "$version" >= "3.4.0" && "$version" < "3.4.5" ]] || \ [[ "$version" >= "4.0.0" && "$version" < "4.2.7" ]]; then echo "Vulnerable: $version" fi done
Upgrade to Patched Version:
npm install [email protected] or for 3.x branch: npm install [email protected] or for 2.x client: npm install [email protected]
Verify Upgrade:
npm list socket.io
Exploit:
A crafted Socket.IO packet is sent with an `attachments` field set to a large number (e.g., 65535) in the packet header. The packet declares binary attachments but the attacker never transmits the actual binary data. The server allocates memory for each declared attachment and waits indefinitely. By sending multiple such packets, the server’s memory is exhausted. No authentication is required, and the attack can be launched remotely.
Protection:
- Immediate Upgrade: Apply the patch by upgrading to Socket.IO
4.2.7,3.4.5, or `3.3.6` depending on the branch in use. - No Workaround: There is no known workaround other than upgrading to a safe version.
- Monitoring: Implement monitoring for unusual memory consumption patterns that might indicate exploitation attempts.
- Supplementary Defenses: Consider implementing connection rate limiting, packet size restrictions, and memory usage monitoring.
Impact:
- Denial of Service: Successful exploitation causes the server to run out of memory, leading to application unresponsiveness or crashes.
- Availability Only: There is no impact on confidentiality or integrity; only availability is affected.
- Critical Environments: Applications processing large volumes of binary data or running in cloud environments with constrained memory are especially at risk.
- Wide Exposure: Affects all versions prior to the patched releases, making a large number of deployments vulnerable.
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Sources:
Reported By: github.com
Extra Source Hub:
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