CVE-2026-102050

Executive Summary

CVE-2026-102050 is a stack-based buffer overflow (CWE-121) in the l2cpd Layer 2 Control Protocol daemon of Juniper Networks Junos OS and Junos OS Evolved. An unauthenticated attacker on an adjacent network segment can trigger the flaw by sending crafted LLDP packets to an interface that has LLDP enabled, causing a denial of service and repeated triggers may disrupt LLDP and other Layer 2 control protocols across the device. No vendor patch, workaround, PoC, or exploitation-in-the-wild evidence is currently documented in the available data.

Technical Analysis

The vulnerability resides in l2cpd, the Juniper daemon responsible for Layer 2 control-plane protocol processing — including LLDP, which is used for neighbor discovery and topology advertisement on a link-local basis. The flaw is classified as a stack-based buffer overflow (CWE-121), which occurs when a fixed-size stack buffer is populated with data whose length exceeds the allocated capacity, and the excess bytes overwrite adjacent stack memory such as saved frame pointers and return addresses.

In this case, the trigger path is incoming LLDP packets. LLDP frames are layer-2 Ethernet frames identified by a distinct EtherType (LLDP) and are structured as a sequence of Type-Length-Value (TLV) elements, each carrying a variable-length payload. LLDP is by design an unauthenticated, unencapsulated protocol: any host on the same broadcast domain can transmit LLDP frames toward a switch or router interface, and the receiving device processes them without requiring any credentials or session state. The NVD description indicates that when such a packet is received on an interface configured for LLDP, the l2cpd daemon processes it in a manner that overflows a stack buffer. The description does not disclose the specific TLV, parsing routine, or code construct involved, so exact code-level mechanics cannot be stated without speculation.

Two characteristics are important for defenders:

1. Unauthenticated, adjacent attack surface. The CVSS vector AV:A/AC:L/PR:N/UI:N confirms the attacker requires only adjacency (same Layer 2 segment, VLAN, or broadcast domain) and no privileges or user interaction. The attack complexity is Low, meaning no special conditions beyond sending the crafted LLDP frame are described.
2. Control-plane, not data-plane, impact. The affected daemon handles Layer 2 control protocols. A crash or memory-corruption-induced fault in l2cpd degrades or halts protocol processing coordinated by that daemon. The description explicitly warns that repeated triggering "may disrupt LLDP and other Layer 2 control protocols across the device," implying the daemon's failure can affect multiple L2 control functions beyond LLDP itself.

The CVSS subscores (C:H/I:H/A:H) reflect that a buffer overflow in a long-running network daemon carries the theoretical potential for confidentiality and integrity compromise in addition to availability; however, the NVD description frames the demonstrated and described outcome primarily as denial of service.

Exploitation Scenarios

No public PoC or exploit code is available for CVE-2026-102050, and no exploitation-in-the-wild evidence has been documented. The following chain is inferred strictly from the vulnerability class (stack-based buffer overflow in LLDP packet processing) and the facts stated in the NVD description.

1. Reconnaissance / target identification. The attacker establishes presence on a network segment adjacent to the target device — for example, a compromised host on an access VLAN, a rogue device connected to an access port, a virtual machine on the same hypervisor bridge, or an attacker on a shared Layer 2 WAN/metro segment. The attacker identifies interfaces where LLDP is enabled. Since LLDP frames are broadcast to a well-known multicast MAC address and are not encrypted or authenticated, the attacker can passively observe existing LLDP advertisements from the target device and other neighbors to confirm that LLDP is active on the segment. Alternatively, the attacker may simply transmit LLDP frames and observe responses or device behavior.

2. Triggering the flaw. The attacker crafts an LLDP Ethernet frame containing TLV structures designed to induce the parsing path in l2cpd that overflows a fixed-size stack buffer. Because the overflow is stack-based, the trigger is a malformed or oversized LLDP payload exceeding the buffer capacity in the affected parsing routine. The precise TLV type, field, and byte layout that cause the overflow are not disclosed in the available data. The frame is transmitted to the target device's LLDP-enabled interface; no authentication, handshake, or prior session is required (PR:N, UI:N, AC:L in the CVSS vector).

3. Payload / execution method (vulnerability-class level). At the level of the vulnerability class, a stack-based buffer overflow can be exploited either as a pure availability fault (corrupting adjacent stack data and crashing the daemon or the processing context) or, in principle, as a control-flow hijack if the overflow can be shaped to overwrite a saved return address or equivalent control structure. The available description describes only the denial-of-service outcome; no information is provided about mitigations such as stack canaries, ASLR, or the exploitability of the overflow toward code execution. The payload-delivery mechanism is simply a network frame delivered on the local segment; no file upload, HTTP request, or user interaction is involved.

4. Post-exploitation impact. Successful triggering causes a fault in the l2cpd daemon, resulting in a denial of service for Layer 2 control-plane processing. The description states that repeated triggering "may disrupt LLDP and other Layer 2 control protocols across the device." In operational terms, disruption of LLDP can blind topology discovery and automated provisioning systems, and broader disruption of L2 control protocols on the device can affect protocol-dependent network operations. Because the CA:H/I:H/A:H subscores apply, a successful memory-corruption exploit could theoretically extend beyond availability, but no public evidence indicates code execution has been achieved.

The attacker's cost is low: adjacency plus the ability to send Ethernet frames. There is no described requirement for any special position beyond the same Layer 2 domain.

Impact Assessment

The CVSS v3.1 base score is 8.8 (High) with vector CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Breaking this down:

• AV:A (Adjacent): exploitation requires the attacker to be on the same Layer 2 domain or an adjacent network path to the target interface. This is a meaningful barrier in segmented environments but is frequently satisfiable in access networks, data centers, service provider edges, and lab environments.
• AC:L (Low): no special conditions are described for the attack beyond delivering the crafted packet.
• PR:N / UI:N: no authentication and no user interaction are required, maximizing the attacker pool among adjacent parties.
• S:U (Unchanged): impact is scoped to the vulnerable device rather than crossing an authorization boundary to other components.
• C:H / I:H / A:H: reflects the theoretical full compromise potential of a memory-corruption defect in a privileged network daemon. The described, demonstrated impact is denial of service; the high confidentiality and integrity subscores should be treated as the upper bound inherent to the vulnerability class, not as confirmed outcomes.

Affected systems. Devices running Juniper Networks Junos OS or Junos OS Evolved with l2cpd active and LLDP enabled on at least one interface. These are typically switches, routers, and security platforms running Junos where LLDP is configured. Exact affected version ranges and exact fixed versions are not available in the provided data (Affected Versions list is empty; no vendor fix recorded).

Blast radius. The primary blast radius is the vulnerable device and its Layer 2 control-plane operations. The NVD description warns that repeated triggering may disrupt LLDP and other Layer 2 control protocols across the device, which can cascade into neighboring devices that depend on LLDP-based topology discovery, automation, and monitoring. Because the attack originates from an adjacent position and requires no authentication, a single compromised or rogue endpoint in an access segment can repeatedly disrupt a device. In environments that permit LLDP across trust boundaries, exposure is broader.

Business impact. Downstream effects include loss of LLDP-based topology visibility for management and orchestration platforms, disruption of automated provisioning, degradation or loss of Layer 2 protocol convergence on the affected device, and operational costs associated with troubleshooting and device restarts. If the controlling vulnerability class is exploitable toward code execution in a specific deployment, the confidentiality and integrity exposure to network telemetry and control-plane data would be material; no such exploitation is documented.

EPSS: Not yet scored by FIRST.org. No EPSS value is asserted here.

CISA KEV: Not listed.

Detection Guidance

Sigma Rule

This rule targets Junos syslog events indicating l2cpd faults or LLDP processing anomalies. Detection is behavioral because no specific malformed-packet signature is disclosed.

title: Juniper Junos l2cpd Daemon Fault or LLDP Processing Anomaly (CVE-2026-102050)
id: 7b3f9a2e-4c1d-4f6a-9e0b-junosl2cpd001
status: experimental
description: Detects Junos log events indicating l2cpd crashes, core dumps, or LLDP processing faults potentially related to CVE-2026-102050.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-102050
author: valtersit.com
date: 2026/01/01
tags:
  - attack.t1498
  - cve.2026.102050
logsource:
  product: juniper
  service: junos
detection:
  selection_daemon:
    - "l2cpd"
    - "l2cp"
  selection_event:
    - "core dump"
    - "core-dump"
    - "segmentation fault"
    - "signal 11"
    - "SIGSEGV"
    - "buffer overflow"
    - "crash"
    - "restart"
    - "unexpected exit"
    - "EXITED"
  condition: selection_daemon and selection_event
falsepositives:
  - Planned daemon restarts during maintenance
  - Other unrelatedl2cpd defects
level: high

YARA Rule

Memory or binary scanning rule for detecting stack-overflow-related artifacts in l2cpd core dumps or captured artifacts. No exact exploitation byte pattern is disclosed, so the rule keys on LLDP parsing context and overflow indicators.

rule CVE_2026_102050_Junos_l2cpd_LLDP_Overflow
{
    meta:
        description = "Detects potential exploitation artifacts of CVE-2026-102050 (l2cpd LLDP stack buffer overflow) in captured memory or core dumps"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-102050"
        cve = "CVE-2026-102050"
        date = "2026-01-01"

    strings:
        $lldp_mac = { 01 80 C2 00 00 0E }
        $lldp_eth = { 88 CC }
        $l2cpd = "l2cpd" ascii wide
        $junos_core = "juniper" ascii wide nocase
        $stack_smash = { 41 41 41 41 41 41 41 41 41 41 41 41 }
        $sigsegv = "segmentation fault" ascii nocase

    condition:
        uint32(0) == 0x7F454C46 or uint32(0) == 0x464C457F or true
        and (
            ($lldp_mac and $lldp_eth and $l2cpd)
            or ($l2cpd and $sigsegv)
            or ($l2cpd and $stack_smash)
        )
}

Suricata IDS Rule

Network rule alerting on LLDP frames exhibiting oversized or anomalous TLV structures. The exact malicious field is not disclosed, so the threshold for TLV count/length is heuristic.

alert ether 01:80:C2:00:00:0E any -> any (msg:"CVE-2026-102050 Juniper Junos LLDP oversized/anomalous TLV payload possible l2cpd stack overflow attempt"; ether_proto:0x88cc; dsize:>1500; threshold: type both, track by_src, count 5, seconds 60; classtype:attempted-dos; reference:cve,2026-102050; sid:10205001; rev:1;)

alert ether any any -> any (msg:"CVE-2026-102050 Juniper Junos LLDP high-frequency frame burst possible DoS trigger"; ether_proto:0x88cc; threshold: type both, track by_src, count 50, seconds 10; classtype:attempted-dos; reference:cve,2026-102050; sid:10205002; rev:1;)

Elastic Detection

This EQL rule correlates Junos log events signifying l2cpd failures with adjacency-sourced traffic, using only fields typically present in Junos log ingestion.

sequence by host.name with maxspan=5m
  [any where event.category == "network" and
     (process.name == "l2cpd" or message : "*l2cpd*") and
     (message : "*crash*" or message : "*core*dump*" or message : "*segmentation fault*" or
      message : "*signal 11*" or message : "*buffer overflow*")]

Splunk SPL Query

index=juniper sourcetype=junos:log ("l2cpd" OR "l2cp") ("crash" OR "core" OR "segmentation fault" OR "signal 11" OR "buffer overflow" OR "restart" OR "EXITED")
| stats count min(_time) as first_seen max(_time) as last_seen values(message) as messages by host
| where count >= 2
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="juniper,junos,cve-2026-102050,">
  <rule id="1020500" level="12">
    <decoded_as>junos</decoded_as>
    <match>l2cpd</match>
    <regex>core dump|segmentation fault|signal 11|SIGSEGV|buffer overflow|EXITED|unexpected restart</regex>
    <description>CVE-2026-102050: Junos l2cpd daemon fault or crash possibly caused by malformed LLDP packet</description>
    <mitre>
      <id>T1498</id>
    </mitre>
  </rule>
  <rule id="1020501" level="10" frequency="3" timeframe="300">
    <if_matched_sid>1020500</if_matched_sid>
    <same_source_ip />
    <description>CVE-2026-102050: Repeated l2cpd faults detected from same source - possible sustained LLDP-based DoS</description>
    <mitre>
      <id>T1498</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix reference, affected-version list, or workaround is documented in the available data. The following guidance is therefore defensive and operational rather than patch-specific.

1) Immediate mitigations

• Disable LLDP on interfaces where it is not operationally required. The vulnerability is triggered via LLDP packets received on an interface configured for LLDP; disabling LLDP on unnecessary interfaces removes the attack surface on those links.
• Where LLDP must remain enabled, restrict Layer 2 adjacency to trusted devices. Enforce port security, 802.1X, MAC limiting, and dynamic ARP/neighbor suppression on access ports so unauthorized hosts cannot inject frames.
• Segment and filter at Layer 2 boundaries. Apply LLDP filtering or traffic suppression on edge/access ports and inter-domain links so LLDP frames from untrusted segments are not forwarded to sensitive or untrusted neighbors.
• Monitor l2cpd health and Junos logs for crashes, core dumps, and unexpected restarts, and treat repeated restarts as a potential active attack.
• Rate-limit or police LLDP control traffic on access and edge interfaces to reduce the impact of burst-triggered DoS (see Suricata/ECS thresholds above for detection context).

2) Patch/upgrade steps

• No patch is currently available per tracked sources. Monitor the Juniper Networks security advisories portal and the NVD entry for CVE-2026-102050 for a fixed Junos OS / Junos OS Evolved release.
• When a vendor fix is published, validate the exact fixed release against the current code train and schedule upgrade during a maintenance window, accounting for control-plane restart of l2cpd.
• Subscribe to Juniper SIRT (Security Incident Response Team) notifications and NVD/CVE feeds to receive patched-version details as soon as they are released.

3) Long-term hardening

• Adopt a least-exposure LLDP policy: enable LLDP only where topology discovery or automation requires it, and only toward trusted neighbors.
• Maintain strict Layer 2 segmentation and control-plane protection to prevent adjacent attackers from reaching sensitive interfaces.
• Enable and centralize Junos logging and telemetry (syslog, streaming telemetry) so l2cpd faults and LLDP anomalies generate reliable alerts mapped to this CVE.
• Establish configuration baselines and periodic audits for LLDP enablement across the fleet, and track patch status for Junos OS and Junos OS Evolved against vendor advisories.
• Exercise incident response for control-plane DoS: predefine containment steps (interface shutdown, LLDP disable, ACL pushes) and maintain out-of-band management access in case in-band management is impacted.

References

• NVD — CVE-2026-102050: https://nvd.nist.gov/vuln/detail/CVE-2026-102050
• Juniper Networks Security Advisories (monitor for the fix for CVE-2026-102050): https://supportportal.juniper.net/s/global-search/security-advisories
• CWE-121 — Stack-based Buffer Overflow: https://cwe.mitre.org/data/definitions/121.html
• CISA Known Exploited Vulnerabilities Catalog (CVE-2026-102050 not listed as of this report): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS (no score published yet for CVE-2026-102050): https://www.first.org/epss/

No threat actor campaigns and no exploit-in-the-wild evidence are documented in the available data for CVE-2026-102050. No public PoC, no Nuclei template, and no exploit code were identified; exploitation details in the Exploitation Scenarios section are inferred from the vulnerability class and the NVD description.