CVE-2026-1526
Published: 12 March 2026
Summary
CVE-2026-1526 is a high-severity Data Amplification (CWE-409) vulnerability in Nodejs Undici. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 6.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SI-10 (Information Input Validation).
Deeper analysis
CVE-2026-1526 is a denial-of-service vulnerability in the undici WebSocket client, stemming from unbounded memory consumption during permessage-deflate decompression. The issue resides in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without enforcing limits on the total decompressed size. This affects Node.js processes using the undici library when handling WebSocket connections that negotiate the permessage-deflate extension.
A remote attacker who controls a malicious WebSocket server can exploit this vulnerability against any undici client that connects and negotiates the extension. By sending a small compressed frame—a "decompression bomb"—that expands to an extremely large size upon decompression, the attacker triggers memory exhaustion in the victim's Node.js process, causing it to crash or become unresponsive. The CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) reflects its network accessibility, low attack complexity, lack of required privileges or user interaction, and high availability impact, mapped to CWE-409 (Improper Handling of Highly Compressed Data).
Mitigation guidance and patches are detailed in related advisories, including the GitHub security advisory for undici (GHSA-vrm6-8vpv-qv8q), the OpenJS Foundation CNA page, and the HackerOne disclosure report 3481206. Additional technical context on permessage-deflate is available in RFC 7692.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-11699
Vulnerability details
The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size.…
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A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive. The vulnerability exists in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Decompression bomb in undici WS client directly enables remote memory exhaustion leading to application crash via crafted compressed frames (T1499.004).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
SC-5 enforces denial-of-service protection mechanisms to limit memory consumption from decompression bombs in WebSocket frames.
SI-2 requires timely identification, reporting, and patching of the unbounded memory accumulation flaw in undici's PerMessageDeflate.decompress() method.
SI-10 mandates validation of decompressed data sizes to ensure they stay within safe thresholds, preventing expansion of malicious compressed frames.