CVE-2026-84378 (GCVE-0-2026-84378)
Vulnerability from cvelistv5 – Published: 2026-09-02 17:54 – Updated: 2026-09-02 19:00
VLAI
EPSS
VEX
Title
HTTPX2: Quadratic SSE line buffering can cause CPU denial of service
Summary
HTTPX2 is a next generation HTTP client for Python. From 2.5.0 until 2.10.0, the HTTPX2 Server-Sent Events parser in src/httpx2/httpx2/_sse.py repeatedly copies and rescans buffered text in _SSELineDecoder.decode() when an attacker-controlled or compromised SSE endpoint splits one unterminated line across many response chunks. The behavior affects httpx2.Client.sse() and httpx2.AsyncClient.sse(), and the total processing work grows quadratically with the line length, allowing a crafted stream to consume excessive CPU and block a synchronous worker or asynchronous event loop. This issue is fixed in version 2.10.0.
Severity
5.9 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-02 19:00 UTC
CWE
- CWE-407 - Inefficient Algorithmic Complexity
Assigner
References
5 references
| URL | Tags |
|---|---|
| https://github.com/pydantic/httpx2/security/advis… | x_refsource_CONFIRM |
| https://github.com/pydantic/httpx2/pull/1071 | x_refsource_MISC |
| https://github.com/pydantic/httpx2/pull/1117 | x_refsource_MISC |
| https://github.com/pydantic/httpx2/commit/cbfc0e0… | x_refsource_MISC |
| https://github.com/pydantic/httpx2/releases/tag/v2.10.0 | x_refsource_MISC |
Impacted products
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-84378",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-09-02T19:00:16.905501Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-09-02T19:00:24.511Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"product": "httpx2",
"vendor": "pydantic",
"versions": [
{
"status": "affected",
"version": "\u003e= 2.5.0, \u003c 2.10.0"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "HTTPX2 is a next generation HTTP client for Python. From 2.5.0 until 2.10.0, the HTTPX2 Server-Sent Events parser in src/httpx2/httpx2/_sse.py repeatedly copies and rescans buffered text in _SSELineDecoder.decode() when an attacker-controlled or compromised SSE endpoint splits one unterminated line across many response chunks. The behavior affects httpx2.Client.sse() and httpx2.AsyncClient.sse(), and the total processing work grows quadratically with the line length, allowing a crafted stream to consume excessive CPU and block a synchronous worker or asynchronous event loop. This issue is fixed in version 2.10.0."
}
],
"metrics": [
{
"cvssV3_1": {
"attackComplexity": "HIGH",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 5.9,
"baseSeverity": "MEDIUM",
"confidentialityImpact": "NONE",
"integrityImpact": "NONE",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
"version": "3.1"
}
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-407",
"description": "CWE-407: Inefficient Algorithmic Complexity",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-02T17:54:19.431Z",
"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"shortName": "GitHub_M"
},
"references": [
{
"name": "https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cp",
"tags": [
"x_refsource_CONFIRM"
],
"url": "https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cp"
},
{
"name": "https://github.com/pydantic/httpx2/pull/1071",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/pydantic/httpx2/pull/1071"
},
{
"name": "https://github.com/pydantic/httpx2/pull/1117",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/pydantic/httpx2/pull/1117"
},
{
"name": "https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414"
},
{
"name": "https://github.com/pydantic/httpx2/releases/tag/v2.10.0",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/pydantic/httpx2/releases/tag/v2.10.0"
}
],
"source": {
"advisory": "GHSA-f2fp-rgf2-35cp",
"discovery": "UNKNOWN"
},
"title": "HTTPX2: Quadratic SSE line buffering can cause CPU denial of service"
}
},
"cveMetadata": {
"assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"assignerShortName": "GitHub_M",
"cveId": "CVE-2026-84378",
"datePublished": "2026-09-02T17:54:19.431Z",
"dateReserved": "2026-09-01T16:27:58.130Z",
"dateUpdated": "2026-09-02T19:00:24.511Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-84378",
"date": "2026-09-04",
"epss": "0.0032",
"percentile": "0.24457"
},
"nvd": "{\"cve\":{\"id\":\"CVE-2026-84378\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-09-02T18:21:29.153\",\"lastModified\":\"2026-09-02T19:18:07.907\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"HTTPX2 is a next generation HTTP client for Python. From 2.5.0 until 2.10.0, the HTTPX2 Server-Sent Events parser in src/httpx2/httpx2/_sse.py repeatedly copies and rescans buffered text in _SSELineDecoder.decode() when an attacker-controlled or compromised SSE endpoint splits one unterminated line across many response chunks. The behavior affects httpx2.Client.sse() and httpx2.AsyncClient.sse(), and the total processing work grows quadratically with the line length, allowing a crafted stream to consume excessive CPU and block a synchronous worker or asynchronous event loop. This issue is fixed in version 2.10.0.\"}],\"affected\":[{\"source\":\"security-advisories@github.com\",\"affectedData\":[{\"vendor\":\"pydantic\",\"product\":\"httpx2\",\"versions\":[{\"version\":\"\u003e= 2.5.0, \u003c 2.10.0\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":5.9,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"HIGH\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":2.2,\"impactScore\":3.6}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2026-09-02T19:00:16.905501Z\",\"id\":\"CVE-2026-84378\",\"options\":[{\"exploitation\":\"none\"},{\"automatable\":\"no\"},{\"technicalImpact\":\"partial\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-407\"}]}],\"references\":[{\"url\":\"https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/pydantic/httpx2/pull/1071\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/pydantic/httpx2/pull/1117\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/pydantic/httpx2/releases/tag/v2.10.0\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cp\",\"source\":\"security-advisories@github.com\"}]}}",
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-09-02T19:03:46+00:00",
"cve": "CVE-2026-84378",
"id": "CVE-2026-84378",
"initial_release_date": "2026-09-02T17:54:19.431000+00:00",
"product_status:known_affected": "4",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "httpx2: HTTPX2: Denial of Service via crafted Server-Sent Events stream",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-84378.json",
"version": "3"
},
"vulnrichment": {
"containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-84378\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-09-02T19:00:16.905501Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-09-02T19:00:21.442Z\"}}], \"cna\": {\"title\": \"HTTPX2: Quadratic SSE line buffering can cause CPU denial of service\", \"source\": {\"advisory\": \"GHSA-f2fp-rgf2-35cp\", \"discovery\": \"UNKNOWN\"}, \"metrics\": [{\"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 5.9, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"MEDIUM\", \"vectorString\": \"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H\", \"integrityImpact\": \"NONE\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"availabilityImpact\": \"HIGH\", \"privilegesRequired\": \"NONE\", \"confidentialityImpact\": \"NONE\"}}], \"affected\": [{\"vendor\": \"pydantic\", \"product\": \"httpx2\", \"versions\": [{\"status\": \"affected\", \"version\": \"\u003e= 2.5.0, \u003c 2.10.0\"}]}], \"references\": [{\"url\": \"https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cp\", \"name\": \"https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cp\", \"tags\": [\"x_refsource_CONFIRM\"]}, {\"url\": \"https://github.com/pydantic/httpx2/pull/1071\", \"name\": \"https://github.com/pydantic/httpx2/pull/1071\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/pydantic/httpx2/pull/1117\", \"name\": \"https://github.com/pydantic/httpx2/pull/1117\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414\", \"name\": \"https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/pydantic/httpx2/releases/tag/v2.10.0\", \"name\": \"https://github.com/pydantic/httpx2/releases/tag/v2.10.0\", \"tags\": [\"x_refsource_MISC\"]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"HTTPX2 is a next generation HTTP client for Python. From 2.5.0 until 2.10.0, the HTTPX2 Server-Sent Events parser in src/httpx2/httpx2/_sse.py repeatedly copies and rescans buffered text in _SSELineDecoder.decode() when an attacker-controlled or compromised SSE endpoint splits one unterminated line across many response chunks. The behavior affects httpx2.Client.sse() and httpx2.AsyncClient.sse(), and the total processing work grows quadratically with the line length, allowing a crafted stream to consume excessive CPU and block a synchronous worker or asynchronous event loop. This issue is fixed in version 2.10.0.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-407\", \"description\": \"CWE-407: Inefficient Algorithmic Complexity\"}]}], \"providerMetadata\": {\"orgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"shortName\": \"GitHub_M\", \"dateUpdated\": \"2026-09-02T17:54:19.431Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-84378\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-09-02T19:00:24.511Z\", \"dateReserved\": \"2026-09-01T16:27:58.130Z\", \"assignerOrgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"datePublished\": \"2026-09-02T17:54:19.431Z\", \"assignerShortName\": \"GitHub_M\"}",
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
Loading…
Loading…
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.
Loading…
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.
Loading…
Loading…