CVE-2026-82397 (GCVE-0-2026-82397)
Vulnerability from cvelistv5 – Published: 2026-08-31 21:28 – Updated: 2026-08-31 21:28
VLAI
EPSS
VEX
Title
Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop
Summary
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8.
Severity
7.5 (High)
CWE
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/tornadoweb/tornado/security/ad… | x_refsource_CONFIRM |
| https://github.com/tornadoweb/tornado/pull/3704 | x_refsource_MISC |
| https://github.com/tornadoweb/tornado/commit/8d63… | x_refsource_MISC |
| https://github.com/tornadoweb/tornado/releases/ta… | x_refsource_MISC |
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| tornadoweb | tornado |
Affected:
< 6.5.8
|
guessed |
{
"containers": {
"cna": {
"affected": [
{
"product": "tornado",
"vendor": "tornadoweb",
"versions": [
{
"status": "affected",
"version": "\u003c 6.5.8"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8."
}
],
"metrics": [
{
"cvssV3_1": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 7.5,
"baseSeverity": "HIGH",
"confidentialityImpact": "NONE",
"integrityImpact": "NONE",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"version": "3.1"
}
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-400",
"description": "CWE-400: Uncontrolled Resource Consumption",
"lang": "en",
"type": "CWE"
}
]
},
{
"descriptions": [
{
"cweId": "CWE-1284",
"description": "CWE-1284: Improper Validation of Specified Quantity in Input",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-31T21:28:13.958Z",
"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"shortName": "GitHub_M"
},
"references": [
{
"name": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4",
"tags": [
"x_refsource_CONFIRM"
],
"url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4"
},
{
"name": "https://github.com/tornadoweb/tornado/pull/3704",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/tornadoweb/tornado/pull/3704"
},
{
"name": "https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de"
},
{
"name": "https://github.com/tornadoweb/tornado/releases/tag/v6.5.8",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/tornadoweb/tornado/releases/tag/v6.5.8"
}
],
"source": {
"advisory": "GHSA-mpf4-983q-p7j4",
"discovery": "UNKNOWN"
},
"title": "Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop"
}
},
"cveMetadata": {
"assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"assignerShortName": "GitHub_M",
"cveId": "CVE-2026-82397",
"datePublished": "2026-08-31T21:28:13.958Z",
"dateReserved": "2026-08-28T22:00:43.512Z",
"dateUpdated": "2026-08-31T21:28:13.958Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-82397",
"date": "2026-09-01",
"epss": "0.0035",
"percentile": "0.27873"
},
"nvd": "{\"cve\":{\"id\":\"CVE-2026-82397\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-08-31T22:17:22.920\",\"lastModified\":\"2026-08-31T22:17:22.920\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8.\"}],\"affected\":[{\"source\":\"security-advisories@github.com\",\"affectedData\":[{\"vendor\":\"tornadoweb\",\"product\":\"tornado\",\"versions\":[{\"version\":\"\u003c 6.5.8\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":7.5,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-400\"},{\"lang\":\"en\",\"value\":\"CWE-1284\"}]}],\"references\":[{\"url\":\"https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/tornadoweb/tornado/pull/3704\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/tornadoweb/tornado/releases/tag/v6.5.8\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4\",\"source\":\"security-advisories@github.com\"}]}}"
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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