Security readout for executives and security teams
Plain-English summary
A device on the same local network can send malformed LLDP traffic that crashes Juniper's Layer 2 control daemon. Repeated traffic can keep affected network devices in a denial-of-service state. The CVE also states remote code execution may be possible, but the bundle does not provide exploit evidence.
Executive priority
Treat as high priority for Juniper infrastructure on shared or untrusted local networks. The most credible business risk is sustained network disruption; the advisory also states possible RCE. Patch planning should focus first on exposed access and aggregation devices.
Technical view
CVE-2021-0277 is a CWE-125 out-of-bounds read in l2cpd while processing specially crafted LLDP frames. It affects listed Junos OS trains before specified fixed releases and Junos OS Evolved before 20.4R2-EVO. CVSS 3.1 is 8.8 with adjacent attack vector and no privileges required.
Likely exposure
Exposure is limited to affected Juniper devices reachable from the attacker's local broadcast domain. Internet exposure is not implied by the CVSS adjacent vector. Prioritize shared campus, access, lab, data-center, and provider Ethernet segments where untrusted systems may transmit LLDP frames.
Exploitation context
The source bundle does not show CISA KEV listing or confirmed active exploitation. The vulnerability can be triggered by continued receipt and processing of crafted LLDP frames from a local broadcast domain, sustaining l2cpd crashes and denial of service. RCE is described as possible but not evidenced further here.
Researcher notes
The key constraint is adjacency: crafted LLDP frames must come from the local broadcast domain. The provided data does not include packet structure, proof-of-concept status, or exploit telemetry. Avoid assuming exploitation in the wild without KEV or vendor evidence.
Mitigation direction
- Upgrade affected Junos OS releases to the fixed versions listed by Juniper or later.
- Upgrade Junos OS Evolved to 20.4R2-EVO or later where applicable.
- Review Juniper JSA11181 for product-specific workaround or deployment guidance.
- Prioritize devices on local segments exposed to untrusted or unmanaged hosts.
Validation and detection
- Inventory Juniper devices and compare Junos versions against the affected trains and fixed thresholds.
- Identify interfaces or segments where LLDP frames can originate from untrusted local systems.
- Check operational logs for repeated l2cpd crashes or unexplained Layer 2 control-plane instability.
- Confirm upgraded devices run a fixed release specified by Juniper guidance.
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-125: 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-0277 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
- 8.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:N/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:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H2.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://kb.juniper.net/JSA11181CVE reference · x_refsource_CONFIRM
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.
Out-of-bounds Read
Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.