tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-49855
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-14 21:17:02 UTC
Updated2026-07-16 16:19:10 UTC
DescriptionTornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.006910000 probability, percentile 0.487700000 (date 2026-07-20)

Problem Types: CWE-409 | CWE-409 CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Tornadoweb Tornado affected < 6.5.6 Not specified

References

ReferenceSourceLinkTags
github.com/tornadoweb/tornado/commit/ff808b33adc52d89a549376a5e3628e92ab... [email protected] github.com
github.com/tornadoweb/tornado/security/advisories/GHSA-mgf9-4vpg-hj56 [email protected] github.com
github.com/tornadoweb/tornado/pull/3626 [email protected] github.com
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