CVE-2026-103005

Executive Summary

CVE-2026-103005 is a memory allocation flaw (CWE-789, "Memory Allocation with Excessive Size Value") in Elasticsearch that allows an authenticated user holding connector management privileges to crash a cluster node. The attacker creates connector resources containing an excessively large description field, then accesses those resources, causing the node to attempt an uncontrolled heap allocation that exhausts available memory. Successful exploitation results in a denial-of-service condition for the affected node, but requires valid credentials with connector-management permissions, limiting exposure to insiders or compromised low-privilege accounts.

Technical Analysis

The vulnerability resides in Elasticsearch's connector management feature, which is part of the Elasticsearch platform's integration/connector subsystem. Per the NVD description, the flaw is classified as CWE-789: the application allocates memory using a size value that is derived directly from user-supplied input — specifically, the size of a connector resource's description field — without validating or bounding that value against a sane maximum.

Two distinct operations are involved in the attack chain as described:

1. Creation of a connector resource whose description field is excessively large.
2. Subsequent access of that connector resource, at which point the stored value is consumed and used as or in a memory allocation size, triggering the excessive allocation.

The critical defect is the absence of a size check on the description field: the platform accepts an arbitrarily large value at creation time and then trusts it when re-materializing the resource in memory. Because the allocation is driven by the input size, an authenticated attacker can force the JVM heap to grow beyond its configured ceiling. Elasticsearch enforces heap limits (-Xms/-Xmx) and applies back-pressure through circuit breakers; the NVD description states that this path results in exhaustion of available heap memory and a crash of the affected node. When heap exhaustion occurs, the JVM cannot fulfill further allocation requests and the node terminates (either via an OutOfMemoryError or because the node's health checks fail and it is removed from the cluster).

The attack mechanism maps to CAPEC-130 (Excessive Allocation). It is a resource-consumption denial of service: no memory-corruption, no code execution, and no confidentiality or integrity impact are described. The CVSS vector (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) reflects remote reachability, low attack complexity, the requirement for low privileges, no user interaction, unchanged scope, and high availability impact only.

The affected version range was not published in the data available for this report. No function names, API paths, or parameter names beyond the description field were disclosed. No patch has been identified by any tracked source; patch confidence is 0/4 and the vulnerability must be treated as UNPATCHED.

Exploitation Scenarios

No public proof-of-concept, Nuclei template, or exploit code exists for this CVE. The attack chain below is inferred strictly from the vulnerability class (CWE-789 / CAPEC-130) and the details in the NVD description. No specific endpoints, request bodies, or code patterns are asserted because none were disclosed.

1. Reconnaissance / target identification. The attacker identifies a reachable Elasticsearch cluster. Elasticsearch nodes commonly listen on TCP/9200 (HTTP/REST) and TCP/9300 (transport), and are frequently exposed to internal networks or the public internet where misconfigured. Elasticsearch advertises itself with distinctive HTTP responses ("You Know, for Search") and product:Elasticsearch can be located via Shodan. The attacker determines whether authentication is enabled and whether their account carries connector-management privileges.

2. Privilege precondition. The vulnerability requires an authenticated user with connector management privileges. This is a deliberate access-control boundary: the attacker must either be a legitimate operator over-provisioned with connector rights, or must have compromised such an account. Once those privileges are held, the flaw is triggered through normal, documented connector-management operations — no privilege escalation is needed.

3. Trigger. The attacker issues the connector-creation operation with a description field set to an excessively large value. The platform stores the resource. Because no upper bound is enforced on the description, the oversized value is persisted. The attacker then accesses the created connector resource, causing Elasticsearch to consume the stored value in a memory-allocation path sized by the field's length. The allocation is uncontrolled and grows the heap toward its configured maximum.

4. Post-exploitation impact. As heap is exhausted, the node's ability to serve requests degrades and circuit breakers may trip; ultimately the node crashes and becomes unavailable. In a multi-node cluster, the attacker can repeat the sequence to crash additional nodes. The business impact is availability loss: search, indexing, and dependent applications fail, and operator intervention (restart, reallocation) is required. There is no described data theft, data modification, or persistent access outcome.

Note: Because no patch, PoC, or advisory detail beyond the NVD description is available, the exact request syntax, connector API path, and the precise allocation code path are unknown. Defenders should treat the description field on connector resources as an untrusted, potentially hostile input and monitor for abnormal sizes.

Impact Assessment

The CVSS v3.1 base score is 6.5 (Medium) with vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. Subscore reading:

• Confidentiality: None — no data disclosure is described.
• Integrity: None — no data is modified or corrupted; the connector resource is legitimately created by a privileged user.
• Availability: High — heap exhaustion crashes the affected node, causing a complete loss of availability for that node.
• Attack Vector: Network, Attack Complexity: Low, Privileges Required: Low, User Interaction: None, Scope: Unchanged.

Blast radius. The immediate victim is the Elasticsearch node that services the connector access. In a clustered deployment, crashing one node shifts load to peers; repeated triggering can cascade to multiple nodes and, in the extreme, make the cluster unavailable. Any application, dashboard, or downstream service that depends on that cluster inherits the outage. Because the trigger requires authenticated connector-management privileges, the most likely threat actors are malicious or negligent insiders, and external attackers who have already obtained a low-privilege account through credential theft or a separate compromise. The vulnerability is not remotely exploitable by an anonymous attacker and does not appear in CISA KEV, indicating no confirmed in-the-wild exploitation at the time of reporting. EPSS has not yet scored this CVE; no probability-of-exploitation figure is asserted here.

Detection Guidance

Detection must focus on (a) abnormal description field sizes on connector resources and (b) JVM heap/OutOfMemoryError telemetry from Elasticsearch nodes. Because no vendor endpoint names were disclosed, rules target field size and node-health signals rather than specific API paths.

Sigma Rule

title: Elasticsearch Connector Resource Created With Excessive Description Field
id: 8f3c1a70-5b2e-4d9a-9c11-7e6a0d4f2b99
status: experimental
description: Detects creation of an Elasticsearch connector resource with an abnormally large description field, consistent with CVE-2026-103005 (CWE-789 excessive memory allocation).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-103005
author: Threat Intelligence
date: 2026/01/01
logsource:
  product: elasticsearch
  service: audit
detection:
  selection_action:
    event.action|contains:
      - 'connector'
  selection_desc:
    - connector.description|re: '^.{10000,}$'
    - description_length|gte: 10000
  condition: selection_action and selection_desc
falsepositives:
  - Legitimate connector descriptions containing large embedded documentation or serialized payloads
level: medium
tags:
  - attack.t1499
  - cwe.789

YARA Rule

rule CVE_2026_103005_Elasticsearch_Oversized_Connector_Description
{
    meta:
        description = "Detects excessively large connector description payloads associated with CVE-2026-103005 (CWE-789) in Elasticsearch"
        author = "Threat Intelligence"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-103005"
        severity = "medium"

    strings:
        $connector = "connector" ascii nocase
        $desc      = "description" ascii nocase
        $pad_a     = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" ascii
        $pad_b     = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" ascii

    condition:
        filesize > 10000 and
        $connector and $desc and
        ($pad_a or $pad_b)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-103005 Elasticsearch Connector Oversized Description Potential DoS"; flow:established,to_server; http.method; content:"POST"; http.request_body; content:"connector"; nocase; content:"description"; nocase; pcre:"/\"description\"\s*:\s*\"[^\"]{10000,}/s"; threshold:type both, track by_src, count 5, seconds 60; classtype:attempted-dos; sid:2026103005; rev:1; reference:cve,CVE-2026-103005; metadata:created_at 2026_01_01, cve CVE-2026-103005;)

Elastic Detection

sequence by user.name with maxspan=5m
  [ any where event.action : "connector-created" and to_long(connector.description_length) >= 10000 ]
  [ any where event.action : "connector-accessed" and process.name : "elasticsearch" ]

Splunk SPL Query

index=elasticsearch sourcetype=elasticsearch:audit OR sourcetype=elastic:audit
(event.action="*connector*" OR message="*connector*")
| eval desc_len = coalesce(connector.description_length, len(description), len(connector_description))
| where desc_len >= 10000
| stats count min(_time) as first_seen max(_time) as last_seen values(event.action) as actions by user.name, host
| where count >= 1
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="elasticsearch,cve-2026-103005,">
  <rule id="1030050" level="10">
    <decoded_as>json</decoded_as>
    <field name="event.action">\.*connector\.*</field>
    <field name="connector.description_length" type="pcre2">^(?:[1-9][0-9]{4,})$</field>
    <description>CVE-2026-103005: Elasticsearch connector resource created with excessively large description field (CWE-789).</description>
    <mitre>
      <id>T1499</id>
    </mitre>
    <group>dos,</group>
  </rule>

  <rule id="1030051" level="12">
    <if_sid>1030050</if_sid>
    <match>OutOfMemoryError</match>
    <description>CVE-2026-103005: Elasticsearch node heap exhaustion following oversized connector description allocation.</description>
    <mitre>
      <id>T1499</id>
    </mitre>
    <group>dos,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No vendor fix, fixed version, or advisory was identified by any tracked source. The following measures reduce exposure but do not eliminate the flaw.

1) Immediate mitigations

• Restrict connector management privileges. Audit all users and roles holding connector-management privileges. Apply least privilege: only explicitly trusted operators should be able to create or modify connector resources.
• Enforce an input size ceiling at the perimeter. Where a reverse proxy, API gateway, or Elasticsearch ingest pipeline sits in front of the cluster, reject connector requests whose description field exceeds a sane maximum (e.g., a few kilobytes). This caps the value before it reaches the vulnerable allocation path.
• Enable and monitor circuit breakers and heap metrics. Ensure Elasticsearch's circuit breakers and JVM heap monitoring are active, and alert on OutOfMemoryError, node-health transitions to red, and abnormal heap growth. These are the earliest reliable signals of exploitation.
• Segment and harden the cluster. Do not expose TCP/9200 or TCP/9300 to untrusted networks. Enforce TLS and authentication everywhere.
• Rotate and review credentials. Because the flaw requires an authenticated account, treat any credential compromise or credential-sharing as a potential DoS enabler, and revoke stale connector-management accounts.

2) Patch / upgrade steps

• No patch exists as of this report. Monitor the official Elastic security advisories and the Elasticsearch release notes for a fixed version. Until a fix is published, do not apply unverified third-party "patches."
• When a vendor fix becomes available: test in a staging cluster, take a snapshot, and roll the upgrade across nodes in a controlled order. Verify that connector description handling is bounded post-upgrade.

3) Long-term hardening

• Adopt a formal input-validation standard that bounds all string fields used in allocation sizing — a control that directly addresses CWE-789 across the platform.
• Enforce resource-consumption limits (heap, request body size, per-field size) as defense-in-depth at both the application and gateway layers.
• Maintain role-based access reviews and automated detection (see Detection Guidance) so that connector-field abuse is caught before heap exhaustion.
• Track CVE-2026-103005 and its CWE classification in your vulnerability-management program and re-prioritize once a fixed version or advisory is released.

References

1. NVD — CVE-2026-103005: https://nvd.nist.gov/vuln/detail/CVE-2026-103005
2. CWE-789 — Memory Allocation with Excessive Size Value: https://cwe.mitre.org/data/definitions/789.html
3. CAPEC-130 — Excessive Allocation: https://capec.mitre.org/data/definitions/130.html
4. Elastic Security Advisories (monitor for a corresponding advisory/fixed version): https://www.elastic.co/community/security
5. CISA Known Exploited Vulnerabilities Catalog (no entry for this CVE at time of reporting): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No threat actor campaigns, exploit-in-the-wild evidence, public PoC, or Nuclei template were identified for CVE-2026-103005. EPSS has not yet assigned a score, and the CVE is not listed in CISA KEV.