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Fencer Vulns
medium 4.7

CVE-2021-36647 json

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

published 2023-01-17 3 y ago modified 2026-07-23 3 mo ago also EUVD-2021-23243 , JLSEC-2025-221

cvss
4.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 6%
public exploits
0
none known

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.

Patch / fix

  • julia MbedTLS_jll 2.27.0+0
  • arm mbed_tls 2.16.11, 2.27.0
  • trustedfirmware mbed_tls 3.0.0
  • mbedtls Debian 14, Debian 13, Debian 12 2.16.11-0.1

debian advisories DEBIAN-CVE-2021-36647

  • fluent-bit CBL-Mariner 2.0 2.0.9-1
  • hvloader CBL-Mariner 2.0 1.0.1-6

azure linux advisories AZL-13023AZL-47713

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
19 mo ago

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
NVD 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
CNA 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
OSV 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
julia MbedTLS_jll
<2.27.0+0
2.27.0+0

Classification

Weakness
  • CWE-327 Use of a Broken or Risky Cryptographic Algorithm

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.