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CVE-2026-82397— Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop

Quick assessment

Affected
tornadoweb tornado
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Tornado 是一个 Python Web 框架和异步网络库。在 6.5.8 版本之前，Tornado 在 中使用 解析 请求体时，未传入 参数。 中的 在调度处理器之前，会通过 中的 和 解析请求体，因此，一个未经身份验证的请求体若包含数百万个由分隔符分隔的字段，会导致单线程事件循环同步阻塞，从而延迟所有连接的处理。请求体大小仅受 限制，其默认值为 104857600 字节。该问题已在 6.5.8 版本中修复。

CVSS 7.5 · High
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I. Basic Information for CVE-2026-82397

Vulnerability Information
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Vulnerability Title
Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop
Source: CVE Program / CVE List V5
Vulnerability Description
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8.
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
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
tornadoweb tornado < 6.5.8 -

II. Public POCs for CVE-2026-82397

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III. Intelligence Information for CVE-2026-82397

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Patches & Fixes for CVE-2026-82397 (2)

Vendor Advisories for CVE-2026-82397 (1)

Vendor Pages for CVE-2026-82397 (1)

IV. Related Vulnerabilities

Same product: tornado
Same vendor: tornadoweb
Same weakness: CWE-400

V. Comments for CVE-2026-82397

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