The vulnerability exists due to a missing size restriction on cumulative data processing within the _GzipMessageDelegate.data_received decompression routines in Tornado. While the framework strictly enforces boundaries for the total incoming compressed file size, it continuously extracts nested data chunks without reviewing the total decompressed size, enabling a malicious server to deploy a "gzip bomb" that drives unlimited system memory allocation and causes a process-wide denial of service (DoS).

The remote SUSE Linux SLED15 / SLED_SAP15 / SLES15 / SLES_SAP15 host has a package installed that is affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:2725-1 advisory.

    This update for python-tornado6 fixes the following issues

    - CVE-2026-49853: authorization header forwarded across cross-origin redirects in SimpleAsyncHTTPClient     (bsc#1268395).
    - CVE-2026-49854: out-of-bounds memory access via C extension (bsc#1268396).
    - CVE-2026-49855: AsyncHTTPClient accumulates decompressed chunks without size limit (bsc#1268397).

Tenable has extracted the preceding description block directly from the SUSE 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 remote SUSE Linux SLED15 / SLED_SAP15 / SLES15 / SLES_SAP15 host has a package installed that is affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:2726-1 advisory.

    This update for python-tornado fixes the following issues

    - CVE-2026-49853: authorization header forwarded across cross-origin redirects in SimpleAsyncHTTPClient     (bsc#1268395).
    - CVE-2026-49854: out-of-bounds memory access via C extension (bsc#1268396).
    - CVE-2026-49855: AsyncHTTPClient accumulates decompressed chunks without size limit (bsc#1268397).

Tenable has extracted the preceding description block directly from the SUSE 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 remote SUSE Linux SLES16 / SLES_SAP16 host has a package installed that is affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:22373-1 advisory.

    This update for python-tornado6 fixes the following issues

    - CVE-2026-49853: authorization header forwarded across cross-origin redirects in SimpleAsyncHTTPClient     (bsc#1268395).
    - CVE-2026-49854: out-of-bounds memory access via C extension (bsc#1268396).
    - CVE-2026-49855: AsyncHTTPClient accumulates decompressed chunks without size limit (bsc#1268397).

Tenable has extracted the preceding description block directly from the SUSE 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 remote openSUSE 16 host has a package installed that is affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21067-1 advisory.

    This update for python-tornado6 fixes the following issues

    - CVE-2026-49853: authorization header forwarded across cross-origin redirects in SimpleAsyncHTTPClient     (bsc#1268395).
    - CVE-2026-49854: out-of-bounds memory access via C extension (bsc#1268396).
    - CVE-2026-49855: AsyncHTTPClient accumulates decompressed chunks without size limit (bsc#1268397).

Tenable has extracted the preceding description block directly from the SUSE 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 version of the Tornado Python library installed on the remote host is prior to 6.5.6. It is, therefore, affected by multiple vulnerabilities:

  - When SimpleAsyncHTTPClient follows a 3xx redirect, it shallow-copies the original HTTPRequest, rewrites     the URL, decrements max_redirects, and removes only the Host header. It does not clear Authorization,     auth_username, auth_password, or auth_mode when the redirect target changes origin. As a result,     credentials intended for one origin can be forwarded to a different origin when follow_redirects=True,     which is the default. (CVE-2026-49853)

  - Tornado's gzip decompression routines work in limited-size chunks, but have no overall limit for the     total size of decompressed chunks that they will accumulate (There has always been a limit for the total     compressed size). This allows a malicious server to consume effectively unlimited amounts of memory if     it is accessed via SimpleAsyncHTTPClient in its default configuration. (CVE-2026-49855)

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

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  CVE-2026-49855


ID	Name	Product	Family	Severity
325033	SUSE SLED15 / SLES15 Security Update : python-tornado6 (SUSE-SU-2026:2725-1)	Nessus	SuSE Local Security Checks	high
325027	SUSE SLED15 / SLES15 Security Update : python-tornado (SUSE-SU-2026:2726-1)	Nessus	SuSE Local Security Checks	high
324858	SUSE SLES16 Security Update : python-tornado6 (SUSE-SU-2026:22373-1)	Nessus	SuSE Local Security Checks	high
324049	openSUSE 16 Security Update : python-tornado6 (openSUSE-SU-2026:21067-1)	Nessus	SuSE Local Security Checks	high
321525	Python Library Tornado < 6.5.6 Multiple Vulnerabilities	Nessus	Misc.	high
443227	SCA: security update for tornado (GHSA-mgf9-4vpg-hj56)	Tenable Cloud Security	SCA Checks	high
443227	SCA: security update for tornado (GHSA-mgf9-4vpg-hj56)	Tenable Self-Hosted Container Security	SCA Checks	high

Detections

Analytics

CVE-2026-49855

high

Tenable Plugins

high

high

high

high

high

high

high