CVE-2026-48106

Executive Summary

CVE-2026-48106 is an application-layer authentication bypass vulnerability in Arc, an open-source, SQL-native time-series database designed for telemetry workloads. The flaw resides in the cluster replication receiver, where the MsgReplicateSync payload is accepted without any application-layer authentication (no HMAC, no signature, no per-message nonce), relying solely on transport-layer TLS/mTLS to secure replication traffic. Any peer that has established a connection on the cluster network can inject, modify, or replay replication messages, potentially leading to unauthorized data replication, data integrity compromise, or denial-of-service conditions. This vulnerability affects all versions of Arc Enterprise prior to 26.06.1 and is currently assessed as unpatchable from public sources, making it a high-priority concern for organizations running cluster-mode deployments.

Technical Analysis

Vulnerability Class: CWE-306 — Missing Authentication for Critical Function

Affected Component: internal/cluster/replication/receiver.go

The vulnerability is rooted in a fundamental flaw in the design of Arc's cluster replication receiver. In the affected file, the receiver validates only the wire-format envelope of inbound messages — specifically checking the message length and opcode fields to ensure the message conforms to expected framing constraints. However, the actual payload, encapsulated in the MsgReplicateSync message type, is accepted without any form of application-layer authentication.

The description explicitly confirms:

• No HMAC (Hash-Based Message Authentication Code) is applied to replication messages.
• No digital signature is used to verify message authenticity.
• No per-message nonce is implemented to prevent replay attacks.

This creates a scenario where the replication stream's only security boundary is the transport layer — specifically TLS or mutual TLS (mTLS). While mTLS does provide strong peer authentication at the network level, the vulnerability description indicates that this does not adequately protect against application-layer tampering or replay once a peer is on the cluster network. In practice, mTLS authenticates the connection, not the message. A compromised or malicious peer that has been granted a valid certificate — or whose certificate is trusted by the cluster — can issue arbitrary MsgReplicateSync messages without any further validation.

Attack Surface: The attack surface is the cluster replication channel itself. Any host that can communicate with the replication receiver port — whether a legitimate but compromised peer, a malicious insider, or an external attacker who has gained access to a valid certificate — can interact with the replication protocol.

Technical Implications:

1. Message Tampering: An attacker with network access can intercept a legitimate MsgReplicateSync message and alter its payload before it reaches the receiver, since there is no integrity check at the application layer.

2. Replay Attacks: Without a nonce or replay protection, an attacker can capture a legitimate replication message and replay it at a later time. This could cause data inconsistencies across cluster nodes, potentially leading to duplicated, reverted, or corrupted telemetry data.

3. Unauthorized Data Injection: An attacker who can connect to the replication channel can send crafted MsgReplicateSync messages containing malicious telemetry data. This could pollute the time-series database, causing incorrect analytics, faulty alerting, or cascading failures in downstream systems that depend on the telemetry data.

4. Trust Boundary Confusion: The vulnerability creates an ambiguity in the trust model — the system treats "authenticated at the transport layer" as equivalent to "authenticated at the application layer," which is a common but dangerous conflation.

Comparison with Proper Design: A robust implementation would apply a Message Authentication Code (MAC) to the MsgReplicateSync payload using a shared secret known only to legitimate cluster peers, include a monotonically increasing nonce or timestamp to prevent replay, and verify both on arrival at the receiver.

Exploitation Scenarios

Based strictly on the NVD description and CVE intelligence data provided, the following attack chain is inferred. No public PoC or exploit code has been identified at the time of this report.

Attack Chain:

Step 1 — Reconnaissance and Target Identification: The attacker first identifies an Arc cluster running a version prior to 26.06.1 with cluster replication mode enabled. Shodan queries such as "product:Arc" or "cluster replication receiver" could be used to locate exposed instances. Alternatively, the attacker may perform internal network reconnaissance from a compromised host already inside the cluster network perimeter.

Step 2 — Triggering the Vulnerability Class: The attacker establishes a connection to the cluster replication port. This could be accomplished through:

• A compromised legitimate peer node whose credentials/certificates have been stolen.
• An external attacker who has gained unauthorized network access to the cluster replication port (if firewalling is misconfigured).
• An insider with access to the cluster network.

Once a TCP connection is established — and mTLS succeeds, if enforced — the attacker crafts a message with a valid wire-format envelope (correct length and opcode fields) containing a MsgReplicateSync payload. The receiver validates the envelope, passes the opcode check, and dispatches the message for processing without any application-layer authentication.

Step 3 — Payload and Execution Method: Since the attack is at the vulnerability-class level and no PoC is available, the exact payload structure cannot be provided. However, by the class nature (missing authentication for replication sync), the attacker would craft a payload that mimics legitimate MsgReplicateSync messages. The content could:

• Request replication of specific data ranges, potentially exfiltrating data from the cluster.
• Inject fabricated telemetry data, corrupting the time-series database.
• If the replication protocol supports deletion or pruning operations, an attacker could attempt to delete historical telemetry data.

Step 4 — Post-Exploitation Impact: Successful exploitation can yield one or more of the following:

• Data Integrity Compromise: Injection of false telemetry into the time-series database, leading to incorrect monitoring dashboards, faulty alerting, and poor operational decision-making.
• Data Exfiltration: Malicious replication requests could be used to harvest sensitive telemetry data that may reveal infrastructure details, application internals, or business-critical metrics.
• Replay-based State Corruption: Replaying captured replication messages could cause nodes to diverge in their data state, leading to conflicts, race conditions, or cascading failures in the replication protocol.
• Availability Impact: Sending malformed or overwhelming replication messages could cause the receiver to crash, enter an error loop, or consume excessive resources, resulting in denial of service.

Note: No public PoC is available at the time of writing. The attack chain described above is inferred strictly from the vulnerability class (CWE-306) and the technical details present in the NVD description. Insufficient technical detail is available regarding the exact structure of the MsgReplicateSync message or the replication protocol to provide more granular exploitation steps.

Impact Assessment

Business Impact:

• Confidentiality: The absence of application-layer authentication permits unauthorized peers to request replication of data, potentially leading to exfiltration of sensitive telemetry. This affects the confidentiality of the time-series data stored in the cluster.
• Integrity: With no HMAC or signature on messages, any peer on the cluster network can tamper with replication payloads. This poses a severe integrity risk — telemetry data is foundational for monitoring, alerting, and analytics, and corrupted data will undermine trust in operational visibility.
• Availability: Replay attacks and malformed message injection can cause node-to-node state divergence, resource exhaustion, or receiver crashes, directly impacting the availability of the database service.

Affected Systems:

• Arc Enterprise deployments running version 26.06.0 or earlier with cluster mode and replication enabled.
• Organizations that deploy Arc in multi-node configurations with distributed telemetry ingestion.
• Systems relying on Arc as a downstream data sink for observability, IoT, or application telemetry.

Blast Radius:

• Within a single cluster, all nodes are at risk because replication is distributed by nature.
• Downstream consumers of the telemetry — analytics pipelines, alerting systems, dashboards — are indirectly impacted by data integrity compromise.
• Organizations with hybrid or multi-cloud deployments are at elevated risk if cluster networking traverses shared infrastructure.

CVSS Context: No CVSS score has been officially assigned (N/A). In the absence of a numeric score, security teams should treat this vulnerability with high severity due to the lack of authentication controls on a critical distributed-system component. The EPSS score has not yet been computed by FIRST.org; do not fabricate an EPSS value.

Detection Guidance

Sigma Rule

title: Suspicious Arc Replication Receiver Traffic
id: 3f8b44c6-9e3a-4f2d-b7b8-5d1a69c784ef
status: experimental
description: Detects anomalous MsgReplicateSync traffic patterns indicative of attempted exploitation of CVE-2026-48106
author: Valtersit Threat Intelligence
date: 2026/06/10
logsource:
  category: application
  product: arc
detection:
  selection:
    event: replication_receiver
    message_type: MsgReplicateSync
  filter_known_peers:
    source_ip:
      - '10.0.0.0/8'
      - '192.168.0.0/16'
      - '172.16.0.0/12'
  condition: selection and not filter_known_peers
level: high
falsepositives:
  - Legitimate replication from newly added cluster nodes
  - Replication traffic from nodes outside pre-configured network ranges (after legitimate network changes)
tags:
  - attack.t1190
  - cve.2026.48106
  - cwe.306

YARA Rule

rule Arc_MsgReplicateSync_Anomaly {
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects anomalous Arc replication receiver messages indicating possible exploitation of CVE-2026-48106"
        date = "2026-06-10"
        cve = "CVE-2026-48106"
        cwe = "CWE-306"
    strings:
        $s_replicate_sync = "MsgReplicateSync" ascii nocase
        $s_receiver_path = "internal/cluster/replication/receiver.go" ascii nocase
        $s_replication = "replication" ascii nocase
        $s_sync = "sync" ascii nocase
        $s_hmac = "hmac" ascii nocase
        $s_auth = "authenticate" ascii nocase
    condition:
        $s_replicate_sync and $s_receiver_path and any of ($s_replication*) and
        not any of ($s_hmac, $s_auth)
}

Suricata IDS Rule

alert tcp any any -> any 9000 (msg:"ET EXPLOIT Arc Replication MsgReplicateSync Suspicious Traffic (CVE-2026-48106)"; flow:established; content:"|0c 00 00 00|"; content:"|01 00 00 00|"; content:"MsgReplicateSync"; nocase; within:500; reference:cve,CVE-2026-48106; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2026-48106; classtype:attempted-admin; sid:2026004810; rev:1;)

Note: The Suricata rule above uses placeholder opcode values. The actual opcode/format for MsgReplicateSync messages is not specified in the CVE description; adjust byte sequences based on protocol analysis of legitimate replication traffic within your environment.

Elastic Detection

sequence by host.ip with maxspan=1m
  [network where event.category == "network_traffic" and
   destination.port == 9000 and
   network.protocol == "tcp" and
   event.action == "accepted"]
  [process where event.action == "exec" and
   process.executable : "*arc*" and
   process.args : "*replication*"]

This rule detects a new connection to the replication port followed by an Arc process execution with replication arguments, potentially indicating a malicious peer connecting to the replication receiver.

Splunk SPL Query

index=arc sourcetype=arc:replication 
| where NOT parent_process IN ("arc-server", "arc-node") 
| table _time, src_ip, dest_ip, msg_type, event
| where msg_type="MsgReplicateSync" AND NOT src_ip IN (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
| stats count by src_ip, dest_ip, _time
| where count > 5
| rename src_ip as "Source IP", dest_ip as "Destination IP", count as "Message Count"

Wazuh OSSEC Rule

<group name="arc,">
  <rule id="907385" level="10">
    <decoded_as>json</decoded_as>
    <field name="msg_type">MsgReplicateSync</field>
    <description>Arc replication receiver accepted MsgReplicateSync from potentially untrusted source</description>
    <group>cve-2026-48106,</group>
    <options>no_full_log</options>
    <match>MsgReplicateSync|receiver</match>
    <regex>\src_ip\.\s+(?!10\.0\.0\.\d+|192\.168\.\d+\.\d+|172\.1[6-9]\.\d+\.\d+)</regex>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Status: Partial patch identified — the vendor lists a fix in version 26.06.1 (listed as 2026.06.1 in the description). However, patch confidence is assessed at 0/4 because no patch evidence is available from any tracked external source, and the affected version list in the CVE data is empty. Security teams should verify the availability of the 26.06.1 release from the official Arc distribution channels.

Immediate Mitigations (to implement today):

1. Restrict Cluster Network Access: Implement strict firewall rules that only permit replication traffic (the port used by internal/cluster/replication/receiver.go) from known-trusted peer IP addresses. Deny all other inbound traffic to the replication port.
2. Audit Replication Logs: Review Arc replication logs for unexpected MsgReplicateSync traffic. Look for messages originating from non-standard source IPs, unusual frequency patterns, or messages observed during maintenance windows when replication is not expected.
3. Disable Cluster Mode: If the cluster functionality is not strictly required for current operations, disable cluster mode entirely. This mitigates the vulnerability by removing the vulnerable component from the attack surface.
4. Enforce Strict mTLS: While mTLS alone is insufficient (as the description confirms), well-configured mTLS with strict certificate pinning can prevent foreign peers from even establishing a connection, reducing the attack surface.
5. Monitor for Anomalous Peer Behavior: Use the detection rules provided above to alert on any replication traffic that does not match expected patterns.

Patch/Upgrade Steps:

1. Monitor the Arc project's release channels for the 26.06.1 release (or any subsequent releases that include the security fix).
2. Before applying the fix, validate the upgrade path in a staging environment that mirrors production cluster topology.
3. Schedule the upgrade during a maintenance window, as cluster replication may be disrupted during the upgrade process.
4. After upgrading to 26.06.1, verify that replication sync messages are now signed/authenticated at the application layer, as described in the release notes.

Long-Term Hardening:

1. Network Segmentation: Place Arc clusters on dedicated network segments with strict ACLs. Do not expose replication ports to general corporate networks.
2. Advanced Authentication: Monitor for adoption of application-layer authentication mechanisms for replication. If HMAC or message signing is added in a future release, use it.
3. Certificate Lifecycle Management: Implement a strong PKI for mTLS with short-lived certificates and automated rotation. Revoke certificates immediately upon suspected compromise.
4. Security Audits: Perform regular security reviews of all internally-developed components, with emphasis on authentication and authorization across all application layers, not just the transport layer.
5. Telemetry Integrity Verification: Deploy independent mechanisms to validate the integrity of time-series data, such as checksums or periodic validation queries, to detect corruption events even if exploitation occurs before detection.

Vendor Coordination: No vendor advisory is listed in the CVE data. If the Arc project maintains a security mailing list or disclosure program, subscribe to receive notifications about this and future vulnerabilities.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-48106 — The official NIST National Vulnerability Database entry providing the vulnerability description, CWE classification (CWE-306), and metadata.

2. Arc Project Repository (affected file reference): The description references internal/cluster/replication/receiver.go in the Arc codebase. Security teams should review this file in their deployed version to understand the exact validation checks performed.

3. CWE-306 Reference: https://cwe.mitre.org/data/definitions/306.html — MITRE Common Weakness Enumeration entry for "Missing Authentication for Critical Function," describing the vulnerability class.

4. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — No known exploitation in the wild at the time of writing (CISA KEV status: NO).

5. MITRE ATT&CK Framework: T1190 — Exploit Public-Facing Application (https://attack.mitre.org/techniques/T1190/) — Primary applicable technique for external attack vector scenarios.

Threat Actor Campaigns: As of the report date, no specific threat actor campaigns targeting this vulnerability have been identified publicly. The EPSS score is not yet computed by FIRST.org, and no PoC or exploit code has been publicly released. However, given the severity of missing authentication in a distributed database component, it is plausible that exploitation attempts may occur once the technical details become more widely disseminated. Monitor threat intelligence feeds and the Arc community for emerging reports.