Security readout for executives and security teams
Plain-English summary
This is a network-reachable denial-of-service flaw in Cisco IOS XR. If exposed IP SLA responder or TWAMP functionality is present, an unauthenticated attacker could exhaust packet memory or crash the IP SLA process, disrupting routing-related processes and device availability. The bundle does not identify affected releases or fixed versions.
Executive priority
Prioritize this for network infrastructure because successful exploitation can degrade router availability and affect routing-related processes. Urgency is highest where IOS XR devices expose IP SLA or TWAMP beyond trusted monitoring networks.
Technical view
CVE-2021-34720 affects Cisco IOS XR Software IP SLA responder and TWAMP features. Mishandled socket creation failures can lead to packet-memory exhaustion or IP SLA process crash. CVSS v3.1 is 8.6, network attack vector, low complexity, no privileges, no user interaction, and high availability impact.
Likely exposure
Likely exposure is Cisco IOS XR devices using or reachable for IP SLA responder or TWAMP traffic. The provided affected-version data is incomplete, so teams should map IOS XR inventory and feature usage against Cisco’s advisory.
Exploitation context
The source bundle says exploitation requires sending specific IP SLA or TWAMP packets to an affected device. It does not cite active exploitation, and KEV status is false. Treat internet- or untrusted-network-reachable management or measurement services as higher risk.
Researcher notes
Root cause is CWE-771 resource allocation without proper release, specifically mishandled socket creation failures in IP SLA and TWAMP processing. Impact is availability only per CVSS, but packet-memory exhaustion can affect other processes, including routing protocols. Version and fix details are not included in the bundle.
Mitigation direction
- Review Cisco advisory for affected releases and fixed software guidance.
- Restrict IP SLA and TWAMP reachability to trusted monitoring sources.
- Disable unused IP SLA responder or TWAMP functionality where operationally safe.
- Prioritize remediation on routing-critical or externally reachable IOS XR devices.
- Monitor device memory and IP SLA process health for abnormal failures.
Validation and detection
- Inventory Cisco IOS XR devices and record software versions.
- Identify devices with IP SLA responder or TWAMP enabled.
- Confirm whether measurement traffic is reachable from untrusted networks.
- Compare inventory and configurations against Cisco’s advisory.
- Review logs and monitoring for packet-memory exhaustion or IP SLA crashes.
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-771: 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-2021-34720 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
- 8.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/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:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.6HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20210908 Cisco IOS XR Software IP Service Level Agreements and Two-Way Active Measurement Protocol Denial of Service 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.
Missing Reference to Active Allocated Resource
Missing Reference to Active Allocated Resource represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.