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High, CVSS 7.5amended

tornado: CurlAsyncHTTPClient enforces no response-size limit — decompression bomb drives unbounded memory accumulation to OOM

CVE-2026-103262GHSA-chx6-46f5-w4vp

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (tornado 6.5.9), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI tornado

    Affected
    <= 6.5.8
    Fixed in
    6.5.9

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-103262: 0.63% estimated exploitation activity in the next 30 days; percentile 50.15 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

An unbounded memory accumulation (decompression bomb) in tornado.curlhttpclient.CurlAsyncHTTPClient — the client-side sibling gap of CVE-2026-49855 — verified end-to-end on the 2026-08-15 master snapshot (6.6.dev1) and present unchanged in the latest release tag v6.5.8 and on master (checked 2026-08-17). When a Tornado application configures the curl client (the documented deployment for proxy support / advanced TLS options) and fetch()es an attacker-chosen or attacker-compromised URL with default decompressresponse=True, a malicious server replying Content-Encoding: gzip with a ~2.8 MB wire bomb drove the client's RSS from 30,884 kB to 1,032,100 kB (~1008 MB) in 3.18 s (~350 MB/s, monotonic, no plateau) until the kernel OOM-killed the process (exit 137, cgroup OOMKilled=true) — with the transfer only 67% complete and no client-side size check ever intervening: curlhttpclient.py contains zero occurrences of maxbodysize/MAXFILESIZE. The identical bomb against the default…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-chx6-46f5-w4vp

  2. Revision 2 · amended ·

    Amended from osv record GHSA-chx6-46f5-w4vp

  3. Revision 1 · created ·

    Published from ghsa record GHSA-chx6-46f5-w4vp

Agent brief

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# Patch Next advisory brief: CVE-2026-103262

Advisory: tornado: CurlAsyncHTTPClient enforces no response-size limit — decompression bomb drives unbounded memory accumulation to OOM
IDs: CVE-2026-103262, GHSA-chx6-46f5-w4vp
Record: https://patchnext.com/advisories/ghsa-chx6-46f5-w4vp (revision 3, source checked 26 Oct 2026, 13:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tornado 6.5.9. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI tornado: affected <= 6.5.8; fixed in 6.5.9

## Suggested inspection (read-only)
- `python -m pip show tornado`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on tornado.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-chx6-46f5-w4vp (GitHub-reviewed advisory GHSA-chx6-46f5-w4vp lists affected ranges: PyPI tornado >=0 <=6.5.8)
- Verified: https://osv.dev/vulnerability/GHSA-chx6-46f5-w4vp (OSV record GHSA-chx6-46f5-w4vp lists affected ranges: PyPI tornado >=0 <6.5.9 (fixed))

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