GHSA-mgf9-4vpg-hj56

Tornado's gzip decompression routines work in limited-size chunks, but have no overall limit for the total size of decompressed chunks that they will accumulate (There has always been a limit for the total compressed size). This allows a malicious server to consume effectively unlimited amounts of memory if it is accessed via SimpleAsyncHTTPClient in its default configuration. HTTPServer is not affected in its default configuration, but it is if decompress_request=True is set.

This bug is fixed in Tornado 6.5.6. max_body_size is now checked both for the compressed and cumulative decompressed size of the response.

Prior to upgrading, this issue can be mitigated by setting decompress_response=False or using CurlAsyncHTTPClient.

Database specific

{
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-15T20:19:28Z",
    "nvd_published_at": null,
    "severity": "HIGH",
    "cwe_ids": [
        "CWE-409"
    ]
}

References

Affected packages

PyPI / tornado

Package

Name: tornado; View open source insights on deps.dev
Purl: pkg:pypi/tornado

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0Unknown introduced version / All previous versions are affected

Fixed

6.5.6

Affected versions

0.*

0.2

1.*

1.0

1.1

1.1.1

1.2

1.2.1

2.*

2.0

2.1

2.1.1

2.2

2.2.1

2.3

2.4

2.4.1

3.*

3.0

3.0.1

3.0.2

3.1

3.1.1

3.2

3.2.1

3.2.2

4.*

4.0

4.0.1

4.0.2

4.1b2

4.1

4.2b1

4.2

4.2.1

4.3b1

4.3b2

4.3

4.4b1

4.4

4.4.1

4.4.2

4.4.3

4.5b1

4.5b2

4.5

4.5.1

4.5.2

4.5.3

5.*

5.0a1

5.0b1

5.0

5.0.1

5.0.2

5.1b1

5.1

5.1.1

6.*

6.0a1

6.0b1

6.0

6.0.1

6.0.2

6.0.3

6.0.4

6.1b1

6.1b2

6.1

6.2b1

6.2b2

6.2

6.3b1

6.3

6.3.1

6.3.2

6.3.3

6.4b1

6.4

6.4.1

6.4.2

6.5b1

6.5

6.5.1

6.5.2

6.5.3

6.5.4

6.5.5

Database specific

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-mgf9-4vpg-hj56/GHSA-mgf9-4vpg-hj56.json"