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.

The remote Debian 11 host has packages installed that are affected by multiple vulnerabilities as referenced in the dla-4236 advisory.

    - -------------------------------------------------------------------------     Debian LTS Advisory DLA-4236-1                debian-lts@lists.debian.org     https://www.debian.org/lts/security/                       Andrej Shadura     June 30, 2025                                 https://wiki.debian.org/LTS
    - -------------------------------------------------------------------------

    Package        : mbedtls     Version        : 2.16.9-0.1+deb11u1     CVE ID         : CVE-2021-24119 CVE-2021-36647 CVE-2021-43666 CVE-2021-44732                      CVE-2022-46392

    Multiple vulnerabilities have been fixed in mbedtls, a lightweight crypto and     SSL/TLS library.

    CVE-2021-24119

        A side-channel vulnerability in base64 PEM file decoding allows         system-level (administrator) attackers to obtain information about         secret RSA keys via a controlled-channel and side-channel attack on         software running in isolated environments that can be single stepped,         especially Intel SGX.

    CVE-2021-36647

        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 allowed 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.

    CVE-2021-43666

        In the mbedtls_pkcs12_derivation function an input password's length         is 0 caused a denial of service.

    CVE-2021-44732

        Function mbedtls_ssl_set_session() performed a double free in certain         out-of-memory conditions.

    CVE-2022-46392

        An adversary with access to precise enough information about memory         accesses (typically, an untrusted operating system attacking a         secure enclave) could recover an RSA private key after observing the         victim performing a single private-key operation, if the window size         (MBEDTLS_MPI_WINDOW_SIZE) used for the exponentiation is 3 or smaller.

    For Debian 11 bullseye, these problems have been fixed in version     2.16.9-0.1+deb11u1.

    We recommend that you upgrade your mbedtls packages.

    For the detailed security status of mbedtls please refer to     its security tracker page at:
    https://security-tracker.debian.org/tracker/mbedtls

    Further information about Debian LTS security advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://wiki.debian.org/LTS

Tenable has extracted the preceding description block directly from the Debian security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch 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. (CVE-2021-36647)

Note that Nessus relies on the presence of the package as reported by the vendor.

The version of fluent-bit / hvloader installed on the remote CBL Mariner 2.0 host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the CVE-2021-36647 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. (CVE-2021-36647)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Severity
240979	Debian dla-4236 : libmbedcrypto3 - security update	Nessus	Debian Local Security Checks	critical
224000	Linux Distros Unpatched Vulnerability : CVE-2021-36647	Nessus	Misc.	medium
173026	CBL Mariner 2.0 Security Update: fluent-bit / hvloader (CVE-2021-36647)	Nessus	MarinerOS Local Security Checks	medium

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CVE-2021-36647

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