CVE-2026-59881 aio-libs CVE debrief

Who should care

Defenders responsible for AIOHTTP deployments, particularly those using the WebSocket client, should assess exposure and verify version 3.14.2 or later is in use. This includes operators, platform administrators, vulnerability management teams, and security teams. They should review WebSocket client configurations, monitor for unusual consumption patterns, and update to version 3.14.2 or later if vulnerable.

Why it matters

CVE-2026-59881 allows a malicious server to cause unexpected CPU and memory consumption in AIOHTTP WebSocket clients. Defenders should verify AIOHTTP version 3.14.2 or later is in use, review WebSocket client configurations, and monitor for unusual consumption patterns.

• Potential for increased CPU consumption due to improper frame handling
• Potential for increased memory consumption due to improper frame handling
• Need for verification of AIOHTTP version in use
• Need for review of WebSocket client configurations

Technical summary

AIOHTTP's WebSocket client improperly handles frames with the RSV1 bit set when the permessage-deflate extension is not negotiated. This allows a malicious server to cause unexpected CPU and memory consumption. The issue is fixed in version 3.14.2. Defenders should prioritize verifying AIOHTTP version 3.14.2 or later in use, reviewing WebSocket client configurations, and monitoring for unusual CPU and memory consumption patterns. The vulnerability impacts AIOHTTP deployments using the WebSocket client, particularly those with high traffic or sensitive data.

Defensive priority

Defenders should prioritize verifying AIOHTTP version 3.14.2 or later in use, reviewing WebSocket client configurations, and monitoring for unusual CPU and memory consumption patterns.

Recommended defensive actions

• Verify AIOHTTP version 3.14.2 or later is in use
• Review WebSocket client configurations for proper extension negotiation
• Monitor for unusual CPU and memory consumption patterns
• Update to version 3.14.2 or later if vulnerable
• Perform vulnerability assessment for AIOHTTP deployments
• Implement compensating controls for exposed systems
• Track exceptions and retest remediated assets

Evidence notes

The CVE record and NVD entry detail a vulnerability in AIOHTTP's WebSocket client. Evidence is based on official CVE Program and NVD records, as well as source references from the aiohttp GitHub repository. The vulnerability allows a malicious server to cause unexpected CPU and memory consumption due to improper frame handling. Defenders should verify AIOHTTP version 3.14.2 or later is in use and review WebSocket client configurations.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.