High
Security advisory
The in-memory certificate cache in strongSwan before 5.9.4 has a remote integer overflow upon receiving many requests with different certificates to fill the cache and later trigger the replacement of cache entries. The code attempts to select a less-often-used cache entry by means of a random number generator, but this is not done correctly. Remote code execution might be a slight possibility.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2021-41991
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 11:21 UTC · Revision 1
Source evidence
The in-memory certificate cache in strongSwan before 5.9.4 has a remote integer overflow upon receiving many requests with different certificates to fill the cache and later trigger the replacement of cache entries. The code attempts to select a less-often-used cache entry by means of a random number generator, but this is not done correctly. Remote code execution might be a slight possibility.
osv:CVE-2021-41991
Complete source record
{
"id": "7e5c371cb75bd22b04dad95f38c1957ef488672f25cb96711b6d2508da8baa9e",
"url": "https://osv.dev/vulnerability/CVE-2021-41991",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "CVE-2021-41991",
"summary": "The in-memory certificate cache in strongSwan before 5.9.4 has a remote integer overflow upon receiving many requests with different certificates to fill the cache and later trigger the replacement of cache entries. The code attempts to select a less-often-used cache entry by means of a random number generator, but this is not done correctly. Remote code execution might be a slight possibility.",
"evidence": "osv:CVE-2021-41991",
"products": [],
"severity": "high",
"structured": {
"id": "CVE-2021-41991",
"aliases": [
"CVE-2021-41991"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/strongswan/strongswan",
"type": "GIT",
"events": [
{
"introduced": "01a8b40b99a5943a08b1488a1a75c351593b51b7"
},
{
"fixed": "66fa7c959a53cff27c83e7f10331ad24cfdfb0a4"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:strongswan:strongswan:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "4.2.10"
},
{
"fixed": "5.9.4"
}
],
"source": "CPE_RANGE"
},
{
"range": [
{
"fixed": "66fa7c959a53cff27c83e7f10331ad24cfdfb0a4"
}
],
"source": "REFERENCES_TAG",
"original_tag": "5.9.4"
}
]
}
}
],
"versions": [
"5.9.4rc1",
"5.9.4dr3",
"5.9.4dr2",
"5.9.4dr1",
"android-2.3.3-1",
"android-2.3.3",
"5.9.3",
"5.9.3rc1",
"5.9.3dr4",
"5.9.3dr3",
"5.9.3dr2",
"5.9.3dr1",
"5.9.2",
"5.9.2rc2",
"5.9.2rc1",
"5.9.2dr2",
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"5.9.1",
"5.9.1rc1",
"5.9.1dr1",
"5.9.0",
"5.9.0rc1",
"5.9.0dr2",
"5.9.0dr1",
"5.8.4",
"5.8.3",
"5.8.3rc1",
"5.8.2",
"5.8.2rc2",
"5.8.2rc1",
"5.8.2dr2",
"5.8.2dr1",
"5.8.1",
"5.8.1rc2",
"5.8.1dr1",
"5.8.0",
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"5.8.0dr2",
"5.7.2",
"5.7.2rc1",
"5.7.2dr4",
"5.7.2dr3",
"5.7.2dr2",
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"5.3.5",
"5.3.4",
"5.3.4rc1",
"5.3.4dr3",
"5.3.4dr2",
"5.3.4dr1",
"5.3.3",
"5.3.3rc2",
"5.3.3dr6",
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"5.3.3dr4",
"5.3.3dr3",
"5.3.3dr1",
"5.3.2",
"5.3.1",
"5.3.1rc1",
"5.3.1dr1",
"5.3.0",
"5.3.0rc1",
"5.3.0dr1",
"5.2.2",
"5.2.2rc1",
"5.2.2dr1",
"5.2.1",
"5.2.1rc1",
"5.2.1dr1",
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"5.1.3",
"5.1.3rc1",
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"5.0.2dr4",
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"5.0.0",
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"4.6.2",
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"4.2.11",
"4.2.10"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-41991.json"
}
}
],
"modified": "2026-10-20T10:54:02.743596888Z",
"provider": "osv",
"references": [
"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5FJSATD2R2XHTG4P63GCMQ2N7EWKMME5/",
"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WQSQ3BEC22NF4NCDZVCT4P3Q2ZIAJXGJ/",
"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Y3TQ32JLJOBJDB2EJKSX2PBPB5NFG2D4/",
"https://github.com/strongswan/strongswan/releases/tag/5.9.4",
"https://lists.debian.org/debian-lts-announce/2021/10/msg00014.html",
"https://www.debian.org/security/2021/dsa-4989",
"https://cert-portal.siemens.com/productcert/pdf/ssa-539476.pdf",
"https://www.strongswan.org/blog/2021/10/18/strongswan-vulnerability-%28cve-2021-41991%29.html"
],
"provider_metadata": {
"unresolved_ranges": [
{
"cpes": [
"cpe:2.3:o:siemens:scalance_sc646-2c_firmware:*:*:*:*:*:*:*:*"
],
"vendor_product": "siemens:scalance_sc646-2c_firmware",
"extracted_events": [
{
"range": [
{
"fixed": "2.3"
}
],
"source": "CPE_RANGE"
}
]
},
{
"cpes": [
"cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*",
"cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*",
"cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*"
],
"vendor_product": "debian:debian_linux",
"extracted_events": [
{
"range": [
{
"introduced": "9.0"
},
{
"last_affected": "9.0"
},
{
"introduced": "10.0"
},
{
"last_affected": "10.0"
},
{
"introduced": "11.0"
},
{
"last_affected": "11.0"
}
],
"source": "CPE_STRING"
}
]
},
{
"cpes": [
"cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*",
"cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*",
"cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*"
],
"vendor_product": "fedoraproject:fedora",
"extracted_events": [
{
"range": [
{
"introduced": "33"
},
{
"last_affected": "33"
},
{
"introduced": "34"
},
{
"last_affected": "34"
},
{
"introduced": "35"
},
{
"last_affected": "35"
}
],
"source": "CPE_STRING"
}
]
}
]
}
},
"related_cves": [
{
"value": "CVE-2021-41991",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 384829,
"published_at": "2021-10-18T14:15:10.333+00:00"
}