Security readout for executives and security teams
Plain-English summary
This flaw lets a valid, lower-privileged user abuse Cisco IOS XR SSH/SCP handling to read or overwrite files they should not access. For network devices, that can expose sensitive configuration or enable privilege escalation. It requires authentication but has low attack complexity.
Executive priority
Prioritize remediation for internet-facing or broadly reachable IOS XR management planes. The risk is high because authenticated misuse can compromise confidentiality and integrity of network device files, including sensitive configuration.
Technical view
CVE-2021-34718 affects the SSH Server process in Cisco IOS XR Software. Insufficient validation of user-supplied SCP arguments can permit authenticated remote arbitrary file read and write. CVSS 3.1 is 8.1 with high confidentiality and integrity impact, no availability impact, and CWE-88 classification.
Likely exposure
Exposure is most likely on Cisco IOS XR devices where SSH/SCP is reachable and lower-privileged accounts can authenticate. The source bundle does not provide specific affected or fixed version ranges.
Exploitation context
The provided sources describe authenticated remote exploitation through SCP parameters during login. The bundle does not show CISA KEV listing or other evidence of active exploitation, so active exploitation should not be assumed from this data alone.
Researcher notes
Key unknowns are exact affected releases, fixed versions, and Cisco-stated workarounds, which are not included in the source bundle. Do not infer unauthenticated impact; the CVSS vector and description require low privileges.
Mitigation direction
- Review Cisco's advisory for exact affected and fixed IOS XR releases.
- Upgrade affected IOS XR devices according to Cisco guidance.
- Restrict SSH/SCP access to trusted management networks.
- Limit low-privilege device accounts and enforce least privilege.
- Monitor device logs for unusual SSH/SCP file-transfer activity.
Validation and detection
- Inventory Cisco IOS XR devices and exposed management services.
- Compare installed IOS XR releases against Cisco's advisory.
- Confirm SSH/SCP is not reachable from untrusted networks.
- Review AAA users for unnecessary low-privilege access.
- Check logs for unexpected SCP activity or file changes.
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-88: Command execution behavior lookup
Command injection weaknesses can lead defenders to review execution techniques and command interpreter telemetry. 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 lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-34718 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
- High
- CVSS
- 8.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N2.85.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.1HighVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20210908 Cisco IOS XR Software Arbitrary File Read and Write VulnerabilityCVE 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 Neutralization of Argument Delimiters in a Command ('Argument Injection')
Improper Neutralization of Argument Delimiters in a Command ('Argument Injection') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.