CVE-2026-49855: CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) in tornadoweb tornado
Tornado, a Python web framework and asynchronous networking library, had a vulnerability in its gzip decompression routines prior to version 6.5.6. The routines processed limited-size chunks but did not enforce an overall limit on the total decompressed data size. This allowed a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer with decompress_request=True to consume effectively unlimited memory, leading to a denial of service. The issue is fixed in Tornado version 6.5.6.
AI Analysis
Technical Summary
CVE-2026-49855 describes a vulnerability in Tornado's gzip decompression prior to version 6.5.6. The decompression routines processed data in limited-size chunks but lacked an overall limit on the accumulated decompressed data size. This flaw allows a malicious server to cause excessive memory consumption when accessed by Tornado's SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True. The vulnerability is categorized under CWE-409 (Improper Handling of Highly Compressed Data leading to data amplification). The issue is resolved in Tornado 6.5.6.
Potential Impact
The vulnerability can lead to high memory consumption on affected Tornado clients or servers, potentially causing denial of service due to resource exhaustion. There is no impact on confidentiality or integrity reported. The CVSS 3.1 score is 7.5 (high), reflecting network attack vector, low complexity, no privileges required, no user interaction, and impact limited to availability.
Mitigation Recommendations
Upgrade to Tornado version 6.5.6 or later, where this vulnerability is fixed. Since the vendor advisory confirms the fix in 6.5.6, applying this official update is the recommended remediation. No other mitigations are specified.
CVE-2026-49855: CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) in tornadoweb tornado
Description
Tornado, a Python web framework and asynchronous networking library, had a vulnerability in its gzip decompression routines prior to version 6.5.6. The routines processed limited-size chunks but did not enforce an overall limit on the total decompressed data size. This allowed a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer with decompress_request=True to consume effectively unlimited memory, leading to a denial of service. The issue is fixed in Tornado version 6.5.6.
CVSS v3.1
Score 7.5high
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-49855 describes a vulnerability in Tornado's gzip decompression prior to version 6.5.6. The decompression routines processed data in limited-size chunks but lacked an overall limit on the accumulated decompressed data size. This flaw allows a malicious server to cause excessive memory consumption when accessed by Tornado's SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True. The vulnerability is categorized under CWE-409 (Improper Handling of Highly Compressed Data leading to data amplification). The issue is resolved in Tornado 6.5.6.
Potential Impact
The vulnerability can lead to high memory consumption on affected Tornado clients or servers, potentially causing denial of service due to resource exhaustion. There is no impact on confidentiality or integrity reported. The CVSS 3.1 score is 7.5 (high), reflecting network attack vector, low complexity, no privileges required, no user interaction, and impact limited to availability.
Mitigation Recommendations
Upgrade to Tornado version 6.5.6 or later, where this vulnerability is fixed. Since the vendor advisory confirms the fix in 6.5.6, applying this official update is the recommended remediation. No other mitigations are specified.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-01T22:03:19.640Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a56a08668715ace432de5ea
Added to database: 07/14/2026, 20:48:06 UTC
Last enriched: 07/14/2026, 21:02:30 UTC
Last updated: 07/14/2026, 21:07:20 UTC
Views: 4
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