Security readout for executives and security teams
Plain-English summary
This issue affects certain Cisco routing platforms and could let someone with local authenticated access make the device run unsigned code during boot. It is not described as remotely exploitable or actively exploited in the provided sources, but affected routers may be business-critical network infrastructure.
Executive priority
Treat this as a moderate infrastructure risk. It is not presented as internet-remotely exploitable, but affected routers can support critical connectivity, so validation and vendor-guided upgrade planning should be handled through normal network maintenance windows.
Technical view
CVE-2021-1136 is an image verification weakness, mapped to CWE-347, in Cisco IOS XR on Cisco 8000 Series routers and NCS 540 routers running NCS540L images. The CVSS 3.1 score is 6.7, with local access and high privileges required, but confidentiality, integrity, and availability impacts rated high.
Likely exposure
Exposure is most likely in organizations operating Cisco 8000 Series routers with Cisco IOS XR or Cisco NCS 540 Series routers running IOS XR NCS540L software images. The source bundle does not provide exact affected release ranges.
Exploitation context
The provided sources do not show CISA KEV listing or active exploitation. Exploitation requires an authenticated local attacker with high privileges and affects the boot process, so exposure depends heavily on administrative access controls and device maintenance practices.
Researcher notes
The source bundle identifies the weakness class and CVSS vector but does not include detailed affected release ranges, fixed versions, or workaround text. Avoid assuming exploit availability. Use the Cisco advisory as the authoritative source for release mapping and remediation specifics.
Mitigation direction
- Inventory Cisco 8000 and NCS 540 routers running IOS XR.
- Check Cisco’s advisory for affected releases and vendor-recommended fixed software.
- Prioritize upgrade planning for routers in critical network paths.
- Restrict and monitor privileged local access to router management interfaces.
- Review change-control records for unauthorized image or boot changes.
Validation and detection
- Confirm whether any NCS 540 devices run NCS540L software images.
- Record IOS XR platform, image, and version for each relevant router.
- Compare device versions against Cisco’s advisory guidance.
- Verify privileged local access is limited to authorized administrators.
- Check boot image integrity and recent administrative change history.
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-347: 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-2021-1136 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
- 6.7 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
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:L/PR:H/UI:N/S:U/C:H/I:H/A:H0.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.7MediumVector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20210203 Cisco IOS XR Software for Cisco 8000 Series Routers and Network Convergence System 540 Series Routers Image Verification VulnerabilitiesCVE reference · vendor-advisory, x_refsource_CISCO
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.
Improper Verification of Cryptographic Signature
Improper Verification of Cryptographic Signature represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.