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. 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.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-1526 advisory.

    Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant     names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple     conflicting Content-Length values on the wire.

    Who is impacted:

    *  Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as     flat arrays*  Applications that accept user-controlled header names without case-normalization

    Potential consequences:

    *  Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-     Length headers (400 Bad Request)*  HTTP Request Smuggling: In deployments where an intermediary and     backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the     last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential     hijacking (CVE-2026-1525)

    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. 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. (CVE-2026-1526)

    ImpactWhen an application passes user-controlled input to the upgrade option of client.request(), an     attacker can inject CRLF sequences (\r\n) to:

    *  Inject arbitrary HTTP headers*  Terminate the HTTP request prematurely and smuggle raw data to non-HTTP     services (Redis, Memcached, Elasticsearch)The vulnerability exists because undici writes the upgrade value     directly to the socket without validating for invalid header characters:

    // lib/dispatcher/client-h1.js:1121if (upgrade) {header += `connection: upgrade\r\nupgrade:
    ${upgrade}\r\n`} (CVE-2026-1527)

    ImpactA server can reply with a WebSocket frame using the 64-bit length form and an extremely large     length. undici's ByteParser overflows internal math, ends up in an invalid state, and throws a fatal     TypeError that terminates the process.

    Patches

    Patched in the undici version v7.24.0 and v6.24.0. Users should upgrade to this version or later.
    (CVE-2026-1528)

    ImpactThe undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation     of the server_max_window_bits parameter in the permessage-deflate extension. When a WebSocket client     connects to a server, it automatically advertises support for permessage-deflate compression. A malicious     server can respond with an out-of-range server_max_window_bits value (outside zlib's valid range of 8-15).
    When the server subsequently sends a compressed frame, the client attempts to create a zlib InflateRaw     instance with the invalid windowBits value, causing a synchronous RangeError exception that is not caught,     resulting in immediate process termination.

    The vulnerability exists because:

    *  The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it     falls within the valid range 8-15*  The createInflateRaw() call is not wrapped in a try-catch block*  The     resulting exception propagates up through the call stack and crashes the Node.js process (CVE-2026-2229)

    This is an uncontrolled resource consumption vulnerability (CWE-400) that can lead to Denial of Service     (DoS).

    In vulnerable Undici versions, when interceptors.deduplicate() is enabled, response data for deduplicated     requests could be accumulated in memory for downstream handlers. An attacker-controlled or untrusted     upstream endpoint can exploit this with large/chunked responses and concurrent identical requests, causing     high memory usage and potential OOM process termination.

    Impacted users are applications that use Undici's deduplication interceptor against endpoints that may     produce large or long-lived response bodies.

    PatchesThe issue has been patched by changing deduplication behavior to stream response chunks to     downstream handlers as they arrive (instead of full-body accumulation), and by preventing late     deduplication when body streaming has already started.

    Users should upgrade to the first official Undici (and Node.js, where applicable) releases that include     this patch. (CVE-2026-2581)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-1524 advisory.

    Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant     names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple     conflicting Content-Length values on the wire.

    Who is impacted:

    *  Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as     flat arrays*  Applications that accept user-controlled header names without case-normalization

    Potential consequences:

    *  Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-     Length headers (400 Bad Request)*  HTTP Request Smuggling: In deployments where an intermediary and     backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the     last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential     hijacking (CVE-2026-1525)

    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. 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. (CVE-2026-1526)

    ImpactWhen an application passes user-controlled input to the upgrade option of client.request(), an     attacker can inject CRLF sequences (\r\n) to:

    *  Inject arbitrary HTTP headers*  Terminate the HTTP request prematurely and smuggle raw data to non-HTTP     services (Redis, Memcached, Elasticsearch)The vulnerability exists because undici writes the upgrade value     directly to the socket without validating for invalid header characters:

    // lib/dispatcher/client-h1.js:1121if (upgrade) {header += `connection: upgrade\r\nupgrade:
    ${upgrade}\r\n`} (CVE-2026-1527)

    ImpactA server can reply with a WebSocket frame using the 64-bit length form and an extremely large     length. undici's ByteParser overflows internal math, ends up in an invalid state, and throws a fatal     TypeError that terminates the process.

    Patches

    Patched in the undici version v7.24.0 and v6.24.0. Users should upgrade to this version or later.
    (CVE-2026-1528)

    ImpactThe undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation     of the server_max_window_bits parameter in the permessage-deflate extension. When a WebSocket client     connects to a server, it automatically advertises support for permessage-deflate compression. A malicious     server can respond with an out-of-range server_max_window_bits value (outside zlib's valid range of 8-15).
    When the server subsequently sends a compressed frame, the client attempts to create a zlib InflateRaw     instance with the invalid windowBits value, causing a synchronous RangeError exception that is not caught,     resulting in immediate process termination.

    The vulnerability exists because:

    *  The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it     falls within the valid range 8-15*  The createInflateRaw() call is not wrapped in a try-catch block*  The     resulting exception propagates up through the call stack and crashes the Node.js process (CVE-2026-2229)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-1525 advisory.

    Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant     names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple     conflicting Content-Length values on the wire.

    Who is impacted:

    *  Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as     flat arrays*  Applications that accept user-controlled header names without case-normalization

    Potential consequences:

    *  Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-     Length headers (400 Bad Request)*  HTTP Request Smuggling: In deployments where an intermediary and     backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the     last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential     hijacking (CVE-2026-1525)

    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. 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. (CVE-2026-1526)

    ImpactWhen an application passes user-controlled input to the upgrade option of client.request(), an     attacker can inject CRLF sequences (\r\n) to:

    *  Inject arbitrary HTTP headers*  Terminate the HTTP request prematurely and smuggle raw data to non-HTTP     services (Redis, Memcached, Elasticsearch)The vulnerability exists because undici writes the upgrade value     directly to the socket without validating for invalid header characters:

    // lib/dispatcher/client-h1.js:1121if (upgrade) {header += `connection: upgrade\r\nupgrade:
    ${upgrade}\r\n`} (CVE-2026-1527)

    ImpactA server can reply with a WebSocket frame using the 64-bit length form and an extremely large     length. undici's ByteParser overflows internal math, ends up in an invalid state, and throws a fatal     TypeError that terminates the process.

    Patches

    Patched in the undici version v7.24.0 and v6.24.0. Users should upgrade to this version or later.
    (CVE-2026-1528)

    ImpactThe undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation     of the server_max_window_bits parameter in the permessage-deflate extension. When a WebSocket client     connects to a server, it automatically advertises support for permessage-deflate compression. A malicious     server can respond with an out-of-range server_max_window_bits value (outside zlib's valid range of 8-15).
    When the server subsequently sends a compressed frame, the client attempts to create a zlib InflateRaw     instance with the invalid windowBits value, causing a synchronous RangeError exception that is not caught,     resulting in immediate process termination.

    The vulnerability exists because:

    *  The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it     falls within the valid range 8-15*  The createInflateRaw() call is not wrapped in a try-catch block*  The     resulting exception propagates up through the call stack and crashes the Node.js process (CVE-2026-2229)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. 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. (CVE-2026-1526)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
304617	Amazon Linux 2023 : nodejs24, nodejs24-devel, nodejs24-full-i18n (ALAS2023-2026-1526)	Nessus	Amazon Linux Local Security Checks	critical
304597	Amazon Linux 2023 : nodejs20, nodejs20-devel, nodejs20-full-i18n (ALAS2023-2026-1524)	Nessus	Amazon Linux Local Security Checks	critical
304569	Amazon Linux 2023 : nodejs22, nodejs22-devel, nodejs22-full-i18n (ALAS2023-2026-1525)	Nessus	Amazon Linux Local Security Checks	critical
302064	Linux Distros Unpatched Vulnerability : CVE-2026-1526	Nessus	Misc.	high

Detections

Analytics

CVE-2026-1526

high

Tenable Plugins

critical

critical

critical

high