Vulnerability in tornado (CVE-2026-49855)
Summary
Vulnerability in tornado (CVE-2026-49855). Risk of unauthorized operations or information disclosure. Exploitable via HTTPServer. Mitigation: upgrade to 6.5.6 or later.
Original description
The description as published by the source.
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.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-49855 has been found in tornado.
Attackers can target a specific entry point like HTTPServer over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade tornado to 6.5.6 or later.
If unsure, ask your IT team or search "tornado CVE-2026-49855" on the vendor's site.
CVE-2026-49855 (tornado) — CWE-409 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: HTTPServer / max_body_size / CurlAsyncHTTPClient
Patched: 6.5.6 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-409) exists in tornado. Attackers reach the vulnerable code path via HTTPServer without authentication.
Check the vendor advisory for the affected versions of tornado. Attack surface: HTTPServer / max_body_size / CurlAsyncHTTPClient.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 6.5.6.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'tornado' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'tornado' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
tornadoを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade tornado to 6.5.6ステージング環境で 6.5.6 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Ubuntu UBUNTU-CVE-2026-49855 python-tornado