Is CVE-2026-103262 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-103262 being exploited in the wild.

How severe is CVE-2026-103262?

High severity, with a CVSS score of 7.5, published 1 October 2026.

Which products and versions are affected?

tornado (PyPI) ECOSYSTEM:introduced=0,fixed=6.5.9; Tornado before 6.5.9.

How is CVE-2026-103262 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-103262?

Check whether you run tornado (PyPI) or Tornado at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-103262: Tornado CurlAsyncHTTPClient unbounded memory accumulation in decompression

CVE-2026-103262 · Severity: high · CVSS 7.5 · Published 2026-10-01

Tornado's curl-based HTTP client lacks response size limits, allowing remote attackers to cause denial of service by sending a gzip-compressed decompression bomb. An attacker can send a small compressed payload that expands to gigabytes in memory, exhausting RAM and crashing the application without any client-side size checks intervening.

Technologies: tornado (PyPI), Tornado. Vendors: PyPI, Tornado.

Quick answers

Is CVE-2026-103262 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-103262 being exploited in the wild.
How severe is CVE-2026-103262?: High severity, with a CVSS score of 7.5, published 1 October 2026.
Which products and versions are affected?: tornado (PyPI) ECOSYSTEM:introduced=0,fixed=6.5.9; Tornado before 6.5.9.
Is there a fix for CVE-2026-103262?: Yes. tornado (PyPI): upgrade to 6.5.9 or later. Until then: Configure CurlAsyncHTTPClient with an explicit max_body_size parameter set to a reasonable limit, or disable decompress_response if gzip decompression is not required for your application. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-103262 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-103262?: Check whether you run tornado (PyPI) or Tornado at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

tornado (PyPI): upgrade to 6.5.9 or later
```
pip install "tornado>=6.5.9"
```

Configure CurlAsyncHTTPClient with an explicit max_body_size parameter set to a reasonable limit, or disable decompress_response if gzip decompression is not required for your application.

Technical details

CurlAsyncHTTPClient accumulates decompressed HTTP response bodies in an unbounded BytesIO buffer without enforcing max_body_size limits, unlike SimpleAsyncHTTPClient which implements three size gates (compressed Content-Length, chunked total, and cumulative decompressed size). When decompress_response is enabled (the default), libcurl decompresses payloads before passing them to the write callback, allowing a gzip bomb to expand from kilobytes on the wire to gigabytes in memory at rates exceeding 350 MB/s. The vulnerability requires network-accessible Tornado applications that use CurlAsyncHTTPClient and fetch attacker-influenced URLs.

Affected products

Tornado Tornado before 6.5.9

Identifiers

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

Timeline

2026-09-14: disclosed
2026-09-12: patched

References

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