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CVE-2021-36647

Use of a Broken or Risky Cryptographic Algorithm in the function mbedtls_mpi_exp_mod() in lignum...

4.7 MediumFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Local
Complexity
High
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

0.17%Down 0.7 points since Jan 18, 2023
90%50%10%1%

What each source reports

NVD Score used 4.7

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.

Record
CVE-2021-36647
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-327
Updated
2026-11-02
CVE List 4.7

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.

Record
CVE-2021-36647
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-327
Updated
2026-11-02
EUVDEUVD-2021-23243 4.7

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.

Record
EUVD-2021-23243
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-7wwm-8prx-hpg2 4.7

Use of a Broken or Risky Cryptographic Algorithm in the function mbedtls_mpi_exp_mod() in lignum...

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.

Record
GHSA-7wwm-8prx-hpg2
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-327
Updated
2026-11-02
OSVAZL-13023 4.7

CVE-2021-36647 affecting package fluent-bit for versions less than 2.0.9-1

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.

Record
AZL-13023
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVAZL-47713 4.7

CVE-2021-36647 affecting package hvloader for versions less than 1.0.1-6

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.

Record
AZL-47713
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
Show 4 moreShow less
OSV 4.7

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.

Record
CVE-2021-36647
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVDEBIAN-CVE-2021-36647 4.7

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.

Record
DEBIAN-CVE-2021-36647
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVJLSEC-2025-221 4.7

Use of a Broken or Risky Cryptographic Algorithm in the function `mbedtls_mpi_exp_mod()` in lignum.c...

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.

Record
JLSEC-2025-221
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2021-36647 4.7

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.

Record
UBUNTU-CVE-2021-36647
CVSS 3.1
4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
fluent-bit
Azure Linux:2
 before 2.0.9-1
2.0.9-1
hvloader
Azure Linux:2
 before 1.0.1-6
1.0.1-6
mbedtls
Debian:12
 before 2.16.11-0.1
2.16.11-0.1
mbedtls
Debian:13
 before 2.16.11-0.1
2.16.11-0.1
mbedtls
Debian:14
 before 2.16.11-0.1
2.16.11-0.1
mbedtls
Debian:11
 before 2.16.9-0.1+deb11u1, plus listed versions
2.16.9-0.1
2.16.9-0.1+deb11u1
MbedTLS_jll
Julia
 before 2.27.0+0
2.27.0+0
mbedtls
Ubuntu:16.04:LTS
 All versions, plus listed versions
2.1.2-12.2.0-12.2.1-12.2.1-22.2.1-2ubuntu0.12.2.1-2ubuntu0.22.2.1-2ubuntu0.3
 None known
mbedtls
Ubuntu:Pro:18.04:LTS
 All versions, plus listed versions
2.5.1-1ubuntu12.6.0-12.7.0-22.8.0-12.8.0-1ubuntu0.1~esm1
 None known
mbedtls
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
2.16.2-12.16.3-12.16.4-1ubuntu22.16.4-1ubuntu2+esm1
 None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-36647 is a medium vulnerability (CVSS 4.7) in Arm Mbed Tls, published January 17, 2023. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.17%, the 6th percentile. Fixed in fluent-bit 2.0.9-1.

References

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