CVE-2026-49855
published 2026-07-14CVE-2026-49855: Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but…
PriorityP342high7.5CVSS 3.1
AVNACLPRNUINSUCNINAH
EPSS
0.57%
46.5th percentile
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.
Affected
48 ranges· showing 25
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| ansible-automation-platform-26 | lightspeed-chatbot-rhel9 | — | — |
| ansible-automation-platform-27 | lightspeed-chatbot-rhel9 | — | — |
| clusterlabs | pcs | — | — |
| debian | python-tornado | — | — |
| exploit-intelligence-tech-preview | vulnerability-analysis-rhel9 | — | — |
| keylime | keylime | — | — |
| mta | mta-solution-server-rhel9 | — | — |
| rhelai3 | bootc-cuda-rhel9 | — | — |
| rhelai3 | bootc-gaudi-rhel9 | — | — |
| rhelai3 | bootc-rocm-rhel9 | — | — |
| rhelai3 | disk-image-cuda-rhel9 | — | — |
| rhoai | odh-feature-server-rhel9 | — | — |
| rhoai | odh-llama-stack-core-rhel9 | — | — |
| rhoai | odh-pipeline-runtime-datascience-cpu-py312-rhel9 | — | — |
| rhoai | odh-pipeline-runtime-minimal-cpu-py312-rhel9 | — | — |
| rhoai | odh-pipeline-runtime-pytorch-cuda-py312-rhel9 | — | — |
| rhoai | odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9 | — | — |
| rhoai | odh-pipeline-runtime-pytorch-rocm-py312-rhel9 | — | — |
| rhoai | odh-pipeline-runtime-tensorflow-cuda-py312-rhel9 | — | — |
| rhoai | odh-pipeline-runtime-tensorflow-rocm-py312-rhel9 | — | — |
| rhoai | odh-th06-cpu-torch210-py312-rhel9 | — | — |
| rhoai | odh-th06-cpu-torch291-py312-rhel9 | — | — |
| rhoai | odh-th06-cuda130-torch210-py312-rhel9 | — | — |
| rhoai | odh-th06-cuda130-torch291-py312-rhel9 | — | — |
| rhoai | odh-th06-rocm64-torch291-py312-rhel9 | — | — |
CVSS provenance
nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
ghsa7.5HIGH
vendor_redhat7.5HIGH
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GHSA
tornado: CurlAsyncHTTPClient enforces no response-size limit — decompression bomb drives unbounded memory accumulation to OOM
ghsa·2026-09-30·CVSS 7.5
CVE-2026-49855 [HIGH] CWE-400 tornado: CurlAsyncHTTPClient enforces no response-size limit — decompression bomb drives unbounded memory accumulation to OOM
tornado: CurlAsyncHTTPClient enforces no response-size limit — decompression bomb drives unbounded memory accumulation to OOM
An unbounded memory accumulation (decompression bomb) in `tornado.curl_httpclient.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 `decompress_response=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
GHSA
tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)
ghsa·2026-06-15
CVE-2026-49855 [HIGH] CWE-409 tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)
tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)
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=F
Red Hat
tornado: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption
vendor_redhat·2026-07-14·CVSS 7.5
CVE-2026-49855 [HIGH] CWE-770 tornado: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption
tornado: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.
A flaw was found in Tornado, a Python web framework and asynchronous networking library. Its gzip decompression routines process data in limited-size chunks but do not enforce an overall limit on the total accumulated decompressed data. This vulnerability allows a malicious server t
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-49855 python-pep517: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [epel-all]
bugzilla·2026-08-24·CVSS 7.5
CVE-2026-49855 [HIGH] CVE-2026-49855 python-pep517: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [epel-all]
CVE-2026-49855 python-pep517: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [epel-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.
Bugzilla
CVE-2026-49855 python-flit: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [epel-all]
bugzilla·2026-08-24·CVSS 7.5
CVE-2026-49855 [HIGH] CVE-2026-49855 python-flit: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [epel-all]
CVE-2026-49855 python-flit: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [epel-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.
Bugzilla
CVE-2026-49855 python-flit: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [fedora-all]
bugzilla·2026-08-24·CVSS 7.5
CVE-2026-49855 [HIGH] CVE-2026-49855 python-flit: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [fedora-all]
CVE-2026-49855 python-flit: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption [fedora-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.
Bugzilla
CVE-2026-49855 tornado: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption
bugzilla·2026-07-14·CVSS 7.5
CVE-2026-49855 [HIGH] CVE-2026-49855 tornado: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption
CVE-2026-49855 tornado: Tornado: Denial of Service via uncontrolled gzip decompression memory consumption
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.
2026-07-14
Published