Medium
Security advisory
Use of a Broken or Risky Cryptographic Algorithm in the function mbedtls_mpi_exp_mod() in lignum.c in Mbed TLS Mbed TLS all versions before 3.0.0, 2.27.0 or 2.16.11 allows attackers with access to precise enough timing and memory access information (typically an untrusted operating system attacking a secure enclave such as SGX or the TrustZone secure world) to recover the private keys used in RSA.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2021-36647
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 08:46 UTC · Revision 1
Source evidence
Use of a Broken or Risky Cryptographic Algorithm in the function mbedtls_mpi_exp_mod() in lignum.c in Mbed TLS Mbed TLS all versions before 3.0.0, 2.27.0 or 2.16.11 allows attackers with access to precise enough timing and memory access information (typically an untrusted operating system attacking a secure enclave such as SGX or the TrustZone secure world) to recover the private keys used in RSA.
osv:CVE-2021-36647
Complete source record
{
"id": "d55e006a5ada91ce6c66da93527c309b107082c08191fd0ec2757709c98a59fb",
"url": "https://osv.dev/vulnerability/CVE-2021-36647",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "CVE-2021-36647",
"summary": "Use of a Broken or Risky Cryptographic Algorithm in the function mbedtls_mpi_exp_mod() in lignum.c in Mbed TLS Mbed TLS all versions before 3.0.0, 2.27.0 or 2.16.11 allows attackers with access to precise enough timing and memory access information (typically an untrusted operating system attacking a secure enclave such as SGX or the TrustZone secure world) to recover the private keys used in RSA.",
"evidence": "osv:CVE-2021-36647",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2021-36647",
"aliases": [
"CVE-2021-36647"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/Mbed-TLS/mbedtls",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "aa1d4e097342af799ba80dfb13640efef498227c"
},
{
"introduced": "3f8d78411a26e833db18d9fbde0e2f0baeda87f0"
},
{
"fixed": "f71e2878084126737cc39083e1e15afc459bd93d"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:arm:mbed_tls:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "0"
},
{
"fixed": "2.16.11"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:arm:mbed_tls:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "2.17.0"
},
{
"fixed": "2.27.0"
}
],
"source": "CPE_RANGE"
}
]
}
}
],
"versions": [
"v2.26.0",
"mbedtls-2.26.0",
"v2.16.10",
"mbedtls-2.16.10",
"v2.16.9",
"mbedtls-2.16.9",
"v2.24.0",
"mbedtls-2.24.0",
"v2.16.8",
"mbedtls-2.16.8",
"mbedtls-2.19.1",
"mbedtls-2.16.6",
"mbedtls-2.22.0d0",
"mbedtls-2.16.5",
"mbedtls-2.21.0",
"mbedtls-2.20.0",
"mbedtls-2.16.4",
"mbedtls-2.20.0d0",
"mbedtls-2.16.3",
"mbedtls-2.19.0d2",
"mbedtls-2.19.0",
"mbedtls-2.19.0d1",
"mbedtls-2.16.2",
"mbedtls-2.16.0",
"mbedtls-2.14.0",
"mbedtls-2.13.1",
"mbedtls-2.13.0",
"mbedtls-2.12.0",
"mbedtls-2.11.0",
"mbedtls-2.10.0",
"mbedtls-2.7.0",
"mbedtls-2.9.0",
"mbedtls-2.8.0",
"mbedtls-2.8.0-rc1",
"mbedtls-2.7.0-rc1",
"mbedtls-2.6.0",
"mbedtls-2.6.0-rc1",
"mbedtls-2.5.1",
"mbedtls-2.5.0",
"mbedtls-2.4.0",
"mbedtls-2.2.1",
"yotta-2.3.1",
"mbedtls-2.3.0",
"mbedtls-2.2.0",
"mbedos-release-15-11",
"mbedos-techcon-oob2",
"mbedtls-2.1.2",
"mbedtls-2.1.0",
"mbedtls-2.1.1",
"beta-oob-2",
"mbedtls-2.0.0",
"polarssl-1.3.9",
"polarssl-1.3.8",
"polarssl-1.3.7",
"polarssl-1.3.6",
"polarssl-1.3.5",
"polarssl-1.3.4",
"polarssl-1.3.3",
"polarssl-1.3.2",
"polarssl-1.3.1",
"polarssl-1.3.0",
"polarssl-1.3.0-rc0",
"polarssl-1.2.6",
"polarssl-1.2.5",
"polarssl-1.2.4",
"polarssl-1.2.2",
"polarssl-1.2.1",
"polarssl-1.2.0"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-36647.json"
}
},
{
"ranges": [
{
"repo": "https://github.com/mbed-tls/mbedtls",
"type": "GIT",
"events": [
{
"introduced": "8b3f26a5ac38d4fdccbc5c5366229f3e01dafcc0"
},
{
"fixed": "8df2f8e7b9c7bb9390ac74bb7bace27edca81a2b"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:trustedfirmware:mbed_tls:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "2.28.0"
},
{
"fixed": "3.0.0"
}
],
"source": "CPE_RANGE"
}
]
}
}
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-36647.json"
}
}
],
"modified": "2026-10-24T10:50:07.968996972Z",
"provider": "osv",
"references": [
"https://lists.debian.org/debian-lts-announce/2025/06/msg00034.html",
"https://github.com/ARMmbed/mbedtls/releases/",
"https://kouzili.com/Load-Step.pdf",
"https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2021-07-1"
],
"provider_metadata": {}
},
"related_cves": [
{
"value": "CVE-2021-36647",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 441999,
"published_at": "2023-01-17T21:15:10.88+00:00"
}