Security readout for executives and security teams
Plain-English summary
This flaw can expose RSA private keys in systems using vulnerable Mbed TLS versions, but only under demanding local side-channel conditions. The clearest risk is where an untrusted operating system can observe timing and memory behavior around a secure enclave such as SGX or TrustZone.
Executive priority
Treat this as targeted but important. It is not broadly wormable, yet private-key recovery can undermine trust, signing, and encrypted communications. Prioritize systems using Mbed TLS for RSA keys in enclave or embedded contexts.
Technical view
CVE-2021-36647 is a CWE-327 issue in mbedtls_mpi_exp_mod() in lignum.c. Mbed TLS versions before 3.0.0, 2.27.0, or 2.16.11 may leak enough side-channel information for RSA private-key recovery when precise timing and memory-access observations are available.
Likely exposure
Exposure is most likely in products or services embedding Mbed TLS before 3.0.0, 2.27.0, or 2.16.11, especially enclave or trusted-execution deployments performing RSA private-key operations.
Exploitation context
The CVE record describes a local, high-complexity attack requiring low privileges and precise timing plus memory-access information. The source bundle does not show CISA KEV listing or confirmed active exploitation.
Researcher notes
The public record gives affected version thresholds and attack preconditions, but the bundle does not provide product-specific affected CPEs or evidence of exploitation. Validation should focus on version provenance, RSA use, and enclave threat models.
Mitigation direction
- Upgrade Mbed TLS to 3.0.0, 2.27.0, 2.16.11, or a later supported release.
- Review the Mbed TLS security advisory and release notes for branch-specific guidance.
- Check operating-system vendor advisories for patched downstream packages.
- Prioritize enclave or trusted-execution systems that perform RSA private-key operations.
- If upgrade is blocked, request vendor-supported compensating guidance.
Validation and detection
- Inventory applications, firmware, and packages that embed or link Mbed TLS.
- Confirm the deployed Mbed TLS version from build artifacts, SBOMs, or package metadata.
- Identify whether RSA private keys are processed through vulnerable Mbed TLS code paths.
- Flag SGX, TrustZone, or similar deployments with untrusted-host exposure.
- Verify patched versions in staging before production rollout.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-327: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-36647 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 4.7 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N13.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.7MediumVector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://kouzili.com/Load-Step.pdfCVE reference
- https://github.com/ARMmbed/mbedtls/releases/CVE reference
- https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2021-07-1CVE reference
- https://lists.debian.org/debian-lts-announce/2025/06/msg00034.htmlCVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Use of a Broken or Risky Cryptographic Algorithm
Use of a Broken or Risky Cryptographic Algorithm represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.