# CVE-2021-36647: mbedtls: Use of a Broken or Risky Cryptographic Algorithm in the function mbedtls_mpi_exp_mod() in lignum.c in Mbed TLS Mbed T...

CVE-2021-36647 is fixed in mbedtls on 1 platform, first by DEBIAN-CVE-2021-36647, released January 17, 2023. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-36647
- Priority: Routine
- CVSS: 4.7 (medium)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jan 17, 2023

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | mbedtls Debian 12.15 (bookworm) | 2.16.11-0.1 | [DEBIAN-CVE-2021-36647](https://patchblox.com/security/data/fix/linux/debian-cve-2021-36647.md) | Jan 17, 2023 |
| Linux | mbedtls Debian 13.5 (trixie) | 2.16.11-0.1 | [DEBIAN-CVE-2021-36647](https://patchblox.com/security/data/fix/linux/debian-cve-2021-36647.md) | Jan 17, 2023 |
| Linux | mbedtls Debian 14 | 2.16.11-0.1 | [DEBIAN-CVE-2021-36647](https://patchblox.com/security/data/fix/linux/debian-cve-2021-36647.md) | Jan 17, 2023 |

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Data as of 2026-11-09T07:25:28Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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