High
Synapse vulnerable to federation denial of service via malformed events
Type: advisorySources: OSV
Synapse is an open source Matrix homeserver implementation. A malicious server can craft events which, when received, prevent Synapse version up to 1.127.0 from federating with other servers. The vulnerability has been exploited in the wild and has been fixed in Synapse v1.127.1. No known workarounds are available.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2025-30355
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 6 Nov 2026, 01:25 UTC · Revision 1
Source evidence
Synapse vulnerable to federation denial of service via malformed events
core-osv · Original sourcePublished 27 Mar 2025, 00:59 UTC
Synapse is an open source Matrix homeserver implementation. A malicious server can craft events which, when received, prevent Synapse version up to 1.127.0 from federating with other servers. The vulnerability has been exploited in the wild and has been fixed in Synapse v1.127.1. No known workarounds are available.
osv:CVE-2025-30355
Complete source record
{
"id": "b94e32192243f0a84feb8d86f67008f4fcf43c761f9eb876a1264e8b63e1ca1d",
"url": "https://osv.dev/vulnerability/CVE-2025-30355",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Synapse vulnerable to federation denial of service via malformed events",
"summary": "Synapse is an open source Matrix homeserver implementation. A malicious server can craft events which, when received, prevent Synapse version up to 1.127.0 from federating with other servers. The vulnerability has been exploited in the wild and has been fixed in Synapse v1.127.1. No known workarounds are available.",
"evidence": "osv:CVE-2025-30355",
"products": [],
"severity": "high",
"structured": {
"id": "CVE-2025-30355",
"aliases": [
"CVE-2025-30355",
"GHSA-v56r-hwv5-mxg6",
"PYSEC-2026-1614"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/element-hq/synapse",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "ecc09b15f108a49348777c908af0187cf26d281e"
},
{
"fixed": "2277df2a1eb685f85040ef98fa21d41aa4cdd389"
}
],
"database_specific": {
"extracted_events": [
{
"range": [
{
"introduced": "0"
},
{
"fixed": "1.127.1"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
},
{
"range": [
{
"fixed": "2277df2a1eb685f85040ef98fa21d41aa4cdd389"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "ecc09b15f108a49348777c908af0187cf26d281e"
}
],
"source": "REFERENCES_TAG",
"original_tag": "v1.127.1"
}
]
}
}
],
"versions": [
"v1.127.0",
"v1.127.0rc1",
"v1.126.0rc3",
"v1.126.0rc2",
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],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-30355.json"
}
}
],
"modified": "2026-10-28T02:30:45.607179738Z",
"provider": "osv",
"references": [
"https://github.com/element-hq/synapse/releases/tag/v1.127.1",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/30xxx/CVE-2025-30355.json",
"https://github.com/element-hq/synapse/security/advisories/GHSA-v56r-hwv5-mxg6",
"https://nvd.nist.gov/vuln/detail/CVE-2025-30355",
"https://github.com/element-hq/synapse/commit/2277df2a1eb685f85040ef98fa21d41aa4cdd389"
],
"provider_metadata": {
"cwe_ids": [
"CWE-20"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/30xxx/CVE-2025-30355.json"
}
},
"related_cves": [
{
"value": "CVE-2025-30355",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 513834,
"published_at": "2025-03-27T00:59:27.996+00:00"
}