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CVE-2026-49855— tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)

Quick assessment

Affected
tornadoweb tornado
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Tornado是中国Tornado团队的一款异步网络编程框架。 Tornado 6.5.6之前版本存在资源管理错误漏洞，该漏洞源于gzip解压缩例程未对累计解压块设置整体限制，可能导致恶意服务器消耗无限内存。

CVSS 7.5 · High EPSS 0.61% · P48

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
tornadoweb tornado < 6.5.6 affected
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I. Basic Information for CVE-2026-49855

Vulnerability Information
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Vulnerability Title
tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)
Source: CVE Program / CVE List V5
Vulnerability Description
Tornado 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
对高度压缩数据的处理不恰当(数据放大攻击)
Source: CVE Program / CVE List V5
Vulnerability Title
Tornado 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Tornado是中国Tornado团队的一款异步网络编程框架。 Tornado 6.5.6之前版本存在资源管理错误漏洞，该漏洞源于gzip解压缩例程未对累计解压块设置整体限制，可能导致恶意服务器消耗无限内存。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
tornadoweb tornado < 6.5.6 -

II. Public POCs for CVE-2026-49855

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Reproduced successfully in a real sandbox · Below is the actual recording of building the environment and exploiting the vulnerability.
Reproduction recording is a Pro+ exclusive
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Qwen3.6-35B-A3B · 9259 chars
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III. Intelligence Information for CVE-2026-49855

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Patches & Fixes for CVE-2026-49855 (2)

Vendor Advisories for CVE-2026-49855 (1)

Same Patch Batch · tornadoweb · 2026-07-14 · 3 CVEs total

CVE-2026-49853 7.7 HIGH Tornado: Authorization header forwarded across cross-origin redirects in SimpleAsyncHTTPCl
CVE-2026-49854 5.3 MEDIUM Tornado: Out-of-bounds memory access in C extension

IV. Related Vulnerabilities

Same product: tornado
Same vendor: tornadoweb
Same weakness: CWE-409

V. Comments for CVE-2026-49855

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