CVE-2026-13683

Executive Summary

CVE-2026-13683 is an SQL injection vulnerability (CWE-89) in the EventScheduler API component of Synology DiskStation Manager (DSM), affecting the 7.2.1, 7.2.2, 7.3.2, and 7.4 release trains below their respective fixed builds. Successful exploitation requires network reachability to the DSM management interface plus an authenticated session holding administrator privileges, which substantially narrows the eligible attacker population. Impact is limited to confidentiality of non-sensitive information (CVSS 2.7, C:L only) — there is no integrity or availability effect per the vendor and NVD scoring.

Technical Analysis

The vulnerability class is unambiguous: improper neutralization of special elements used in an SQL command, mapped to CWE-89. Per the NVD description, the injection point resides within the EventScheduler API of Synology DSM. The EventScheduler subsystem governs scheduled/cron-like tasks on the NAS appliance, and its API is consumed by the DSM web management front end.

The following characteristics are directly derivable from the supplied data:

• Attack vector (AV:N): The vulnerable API is reachable over the network, consistent with DSM's web management interface and its JSON/WebAPI surface.
• Privileges required (PR:H): The attacker must already be an authenticated DSM user holding administrator rights. This is not a pre-authentication or privilege-escalation-over-the-wire issue in the classic sense; the injection is reachable by a principal who already holds the highest privilege tier.
• User interaction (UI:N): No victim interaction is required — the attacker drives the request directly.
• Scope (S:U): The impact is confined to the vulnerable component; no cross-boundary scope change is scored.
• Confidentiality (C:L): Only non-sensitive information is exposed according to the description. Integrity (I:N) and Availability (A:N) are unscored, meaning the vulnerability is not assessed to permit data modification or denial of service through the injection itself.

Why the rating is low, and why it still matters

The 2.7 base score is a direct consequence of PR:H plus C:L. In isolation this is a low-severity finding. From a threat-intelligence standpoint, however, several observations remain relevant:

1. SQL injection in a management API is a control-plane issue. Even a read-only, non-sensitive-data leak from the scheduler API confirms that untrusted input reaches a SQL parser. The same code path's resistance to more impactful payload classes (stacked queries, time-based blind inference, UNION-based extraction of adjacent tables) cannot be assumed from the C:L scoring alone — the score reflects the vendor's assessment of what is reachable, not a proof of what is not.
2. Administrator context amplifies any residual risk. A principal with admin rights on a DSM appliance already controls shares, accounts, network settings, and (on many deployments) backup targets. An injection reachable only by such a principal is more accurately characterized as a post-authentication hardening gap than as a perimeter breach vector — but it still represents a control failure that should be closed, particularly in multi-admin or delegated-administration environments where an admin session may be hijacked via CSRF, XSS, or credential theft on an unrelated component.
3. The API surface is broad. Because the description names "EventScheduler API" generically, and no request parameters, endpoint paths, or function names are disclosed, the exact injection parameter cannot be enumerated here. Analysts should not assume any specific parameter name; the authoritative source is Synology's advisory (see References), which was not included in the supplied dataset.

No CVE-level detail on the specific SQL construction pattern (e.g., string concatenation versus ORM misuse) is available in the provided data, and none is fabricated here.

Exploitation Scenarios

Important caveat: No public PoC, exploit code, or Nuclei template exists for CVE-2026-13683 as of this writing. The chain below is described at the vulnerability-class level and is explicitly annotated where inference begins.

Step 1 — Reconnaissance / target identification. An adversary enumerates internet- or WAN-exposed Synology NAS devices, typically via Shodan/Censys using the DSM login banner and favicon signature, or by scanning for exposed DSM management ports. Targets of interest are DSM 7.2.1/7.2.2/7.3.2/7.4 hosts whose build numbers fall below the fixed thresholds listed above. Note that DSM management interfaces are frequently reachable from untrusted networks on small-business and branch deployments, which is why this class of appliance recurs in ransomware targeting.

Step 2 — Establishing the required precondition. The attacker must obtain an authenticated session with administrator privileges on the target DSM. This precondition is scored explicitly (PR:H) and is the dominant constraint on exploitability. Realistic paths include: valid admin credentials obtained via phishing, credential stuffing against the DSM login, reuse of leaked credentials, session token theft from a compromised workstation, or abuse of an already-trusted internal position. Without this, the vulnerability is not reachable per the CVSS model.

Step 3 — Triggering the injection. With an admin session, the attacker issues a crafted request to the EventScheduler API in which a user-supplied field is concatenated into a SQL statement without proper neutralization (CWE-89). Because the description does not disclose the affected parameter or endpoint path, the specific injection point is not named here; it should be confirmed against Synology's advisory or by authorized source review. At the class level, the payload manipulates the SQL grammar of the backend query (e.g., injecting boolean or UNION-style clauses) so that the resulting statement returns data the caller was not intended to receive.

Step 4 — Post-exploitation impact. Per NVD, the achievable outcome is retrieval of non-sensitive information (C:L). No modification of data (I:N) and no service disruption (A:N) are attributed to this issue. Practically, this means the exploitation value to a capable adversary is informational/validation-grade rather than a direct path to full compromise — useful for confirming SQL reachability, mapping backend schema structure, and informing follow-on attacks. It is not, on its own, a ransomware deployment primitive. Analysts should nevertheless treat confirmed exploitation as an indicator that an admin session is in adversary hands, which is a far more serious condition than the injection itself.

Impact Assessment

Business impact. Because exploitation requires an already-authenticated admin, the direct business impact is bounded: an attacker who already holds admin rights on a NAS typically has simpler, higher-yield avenues (file share access, backup repository tampering, account creation, DSM configuration changes) than a read-only, non-sensitive SQL injection. The principal risk is therefore secondary: the vulnerability serves as a quiet confirmation/leakage primitive for an adversary who has already obtained admin access, and it may assist schema discovery that supports later, higher-impact activity.

Affected systems. Synology DiskStation Manager (DSM) on the 7.2.1, 7.2.2, 7.3.2, and 7.4 release trains, below builds 7.2.1-69057-12, 7.2.2-72806-9, 7.3.2-86009-4, and 7.4-90075 respectively. This spans DiskStation (DS/DSM consumer and SMB), RackStation, and larger NAS units running the same DSM branches. No OSV package data was supplied, consistent with DSM being firmware/OS rather than a package-managed ecosystem.

Blast radius. Per event, one appliance. In delegated-administration or MSP environments, a single compromised admin workstation may expose multiple managed DSM instances serially, but the vulnerability itself does not propagate.

Detection Guidance

Detection strategy rests on three pillars: (a) monitoring for anomalous admin sessions hitting the EventScheduler API, (b) request-payload inspection for SQL metacharacters on DSM management traffic, and (c) correlation with credential-theft signals, since PR:H makes anomalous admin activity the true high-signal indicator.

Because no public PoC exists, network signatures must be pattern-based rather than payload-exact; they will generate some false positives against legitimate administrative tooling and should be tuned to your environment.

Sigma Rule

title: Synology DSM EventScheduler API SQL Injection Attempt (CVE-2026-13683)
id: 3d9c1f42-7b6a-4e21-9c0d-cve202613683
status: experimental
description: Detects HTTP requests to the Synology DSM EventScheduler API containing SQL metacharacter patterns, indicative of CVE-2026-13683 exploitation by an authenticated administrator.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-13683
author: valtersit.com Threat Intelligence
date: 2026/01/01
tags:
  - attack.t1190
  - cwe.89
logsource:
  category: webserver
  product: synology
detection:
  selection_endpoint:
    cs-uri-query|contains:
      - 'EventScheduler'
      - 'eventScheduler'
      - 'SYNO.Core.Event'
  selection_sqli:
    cs-uri-query|contains:
      - "'"
      - '"'
      - '--'
      - '/*'
      - 'UNION'
      - 'SELECT'
      - 'OR 1=1'
      - 'SLEEP('
      - 'BENCHMARK('
      - 'EXTRACTVALUE('
  condition: selection_endpoint and selection_sqli
falsepositives:
  - Legitimate administrative scripts passing quoted values in scheduler task names or descriptions
  - Security scanners performing authenticated API fuzzing
level: medium

YARA Rule

rule CVE_2026_13683_Synology_DSM_EventScheduler_SQLi
{
    meta:
        description = "Detects SQL injection payload patterns targeting the Synology DSM EventScheduler API (CVE-2026-13683) in HTTP request captures or web access logs"
        author = "valtersit.com Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-13683"
        cve = "CVE-2026-13683"
        cwe = "CWE-89"
        date = "2026-01-01"

    strings:
        $api1 = "EventScheduler" ascii nocase
        $api2 = "eventScheduler" ascii nocase
        $api3 = "SYNO.Core.Event" ascii nocase

        $sqli1 = "UNION SELECT" ascii nocase
        $sqli2 = "OR 1=1" ascii nocase
        $sqli3 = "' OR '" ascii nocase
        $sqli4 = "SLEEP(" ascii nocase
        $sqli5 = "BENCHMARK(" ascii nocase
        $sqli6 = "EXTRACTVALUE(" ascii nocase
        $sqli7 = "--" ascii
        $sqli8 = "'--" ascii
        $sqli9 = "/*" ascii

    condition:
        (any of ($api*)) and (any of ($sqli*))
}

Suricata IDS Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-13683 Synology DSM EventScheduler API SQL Injection Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"EventScheduler"; nocase; http.uri; content:"SYNO.Core.Event"; nocase; http.client_body; content:"UNION"; nocase; http.client_body; content:"SELECT"; nocase; http.client_body; content:"OR 1=1"; nocase; http.client_body; pcre:"/(%27|'|%22|\")[\s\S]{0,64}(UNION|SELECT|OR\s+1=1|SLEEP|BENCHMARK|EXTRACTVALUE)/i"; metadata:reference nvd.nist.gov/vuln/detail/CVE-2026-13683, created_at 2026_01_01, updated_at 2026_01_01; classtype:web-application-attack; sid:90013683; rev:1;)

Deployment note: DSM management traffic is typically TLS-wrapped. This signature is only usable where TLS inspection or a terminating reverse proxy is in place. Deploy it in detection-only mode initially and tune heavily — legitimate scheduler payloads containing apostrophes will fire it.

Elastic Detection

sequence by source.ip with maxspan=5m
  [ network where
      network.protocol == "http" and
      http.request.method == "POST" and
      http.request.uri : "EventScheduler" ]
  [ network where
      network.protocol == "http" and
      http.request.method == "POST" and
      (
        http.request.body.content : "UNION SELECT" or
        http.request.body.content : "OR 1=1" or
        http.request.body.content : "SLEEP(" or
        http.request.body.content : "BENCHMARK(" or
        http.request.body.content : "EXTRACTVALUE("
      ) ]

A complementary EQL for host-side log correlation, where DSM syslog is forwarded:

any where
  (process.name : "nginx" or process.name : "httpd") and
  message : "*EventScheduler*" and
  (
    message : "*UNION*" or
    message : "*OR 1=1*" or
    message : "*EXTRACTVALUE*" or
    message : "*SLEEP(*"
  )

Splunk SPL Query

index=web OR index=proxy sourcetype=access_combined OR sourcetype=pan:traffic
| eval uri_lower = lower(uri)
| eval body_lower = lower(coalesce(form_data, request_body, ""))
| where (like(uri_lower, "%eventscheduler%") OR like(uri_lower, "%syno.core.event%"))
| where (like(body_lower, "%union%s elect%")
      OR like(body_lower, "%or 1=1%")
      OR like(body_lower, "%sleep(%")
      OR like(body_lower, "%benchmark(%")
      OR like(body_lower, "%extractvalue(%")
      OR like(body_lower, "%'--%"))
| stats count min(_time) as first_seen max(_time) as last_seen
        values(uri) as sample_uris
        values(src_ip) as sources
  by user, src_ip, dest_ip
| where count >= 1
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Tuning guidance: baseline legitimate EventScheduler traffic for 7–14 days before alerting. In most environments the volume is very low, so even a handful of hits with SQL metacharacters warrants investigation.

Wazuh OSSEC Rule

<group name="synology,dsm,web,sql_injection,">
  <rule id="100683" level="0">
    <decoded_as>json</decoded_as>
    <field name="url">\.EventScheduler|SYNO\.Core\.Event</field>
    <description>Synology DSM EventScheduler API request observed (baseline)</description>
  </rule>

  <rule id="100684" level="10" frequency="1" timeframe="300">
    <if_sid>100683</if_sid>
    <field name="url">('|%27|--|UNION|SELECT|OR\+1=1|SLEEP|BENCHMARK|EXTRACTVALUE)</field>
    <description>CVE-2026-13683: Possible SQL injection attempt against Synology DSM EventScheduler API (CWE-89)</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_13683,sqli,</group>
  </rule>

  <rule id="100685" level="12" frequency="5" timeframe="120">
    <if_sid>100684</if_sid>
    <same_source_ip />
    <description>CVE-2026-13683: Repeated SQL injection attempts against DSM EventScheduler API from single source (possible automated exploitation)</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence exists from any tracked source. No vendor fix URL, commit, or advisory reference was supplied. No workarounds were supplied. Treat the following as standing guidance, not as confirmation that a fix is available.

1) Immediate mitigations (do not require the fix):

• Remove DSM management interfaces from untrusted networks. This is the single highest-value control. Restrict DSM admin UI and API access to a management VLAN, VPN, or a source-IP allowlist. Because PR:H requires an existing admin session, eliminating remote reachability removes the network precondition entirely (AV:N → effectively local/trusted-adjacent).
• Reduce the number of administrator accounts. Enforce least privilege, eliminate shared admin credentials, and audit for dormant or orphaned admin accounts. Every unnecessary admin identity is an additional way to satisfy the PR:H precondition.
• Enforce MFA on all DSM administrator accounts and shorten admin session lifetimes. This directly attacks Step 2 of the exploitation chain.
• Monitor for admin session anomalies. Alert on admin logins from new ASNs/geographies, at unusual hours, or after repeated failed authentications. This is the detection with the highest true-positive value for this CVE.
• Constrain the EventScheduler component if your DSM build allows disabling unused scheduled-task features, and log all EventScheduler API activity at the reverse-proxy/WAF layer where TLS termination is possible.
• Deploy a WAF rule blocking SQL metacharacter sequences in requests to DSM API paths; treat it as compensating control only.

2) Patch / upgrade steps:

• Because patch confidence is 0/4, the fixed builds named in the NVD description should be treated as reference boundaries, not as confirmed-available releases. Validate availability against Synology's official DSM Release Notes and Security Advisory pages before scheduling maintenance.
• If a matching fixed build (7.2.1-69057-12, 7.2.2-72806-9, 7.3.2-86009-4, or 7.4-90075 or later) is confirmed available for your hardware platform, follow standard Synology upgrade procedure: snapshot/back up configuration, verify platform support, apply during a maintenance window.
• Track Synology's advisory feed continuously; this entry may be updated with a vendor reference.

3) Long-term hardening:

• Adopt a formal NAS/appliance patch-management cadence — firmware-bound systems are chronically under-patched, and DSM is a recurring ransomware target class.
• Integrate DSM audit logs and API access logs into the SIEM with the detection rules above enabled and baselined.
• Include NAS management planes in red-team scoping: post-authentication SQL injection and other control-plane flaws are systematically under-tested.
• Enforce network segmentation so that compromise of a DSM appliance cannot pivot laterally to hypervisors, backup repositories, or identity infrastructure.
• Where supported, deploy DSM behind an authenticating reverse proxy with TLS inspection so network-layer detection (Suricata/Elastic) is actually effective for this and future control-plane CVEs.

References

1. NVD — CVE-2026-13683: https://nvd.nist.gov/vuln/detail/CVE-2026-13683
2. MITRE CWE-89 — Improper Neutralization of Special Elements used in an SQL Command: https://cwe.mitre.org/data/definitions/89.html
3. Synology Security Advisory portal (vendor bulletin for this CVE was not included in the supplied dataset; consult the official Synology security advisory index and DSM release notes to confirm fixed-build availability): https://www.synology.com/en-global/security/advisory
4. MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
5. CISA Known Exploited Vulnerabilities Catalog — CVE-2026-13683 is NOT listed as of this report; no exploit-in-the-wild evidence is available in the supplied data: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat actor / exploit-in-the-wild note: No public PoC, exploit code, or Nuclei template exists for CVE-2026-13683 per the supplied data. CISA KEV status is NO. No threat actor campaigns are associated with this CVE in any available source. The low base score (2.7), high privilege precondition (PR:H), and non-sensitive-only confidentiality impact (C:L) make weaponization and mass exploitation unlikely — the realistic risk profile is post-authentication misuse by an adversary who has already obtained administrator credentials, not opportunistic internet-wide scanning. Monitoring for compromised admin sessions remains a higher-yield defensive posture for this CVE than signature-based pre-auth exploit detection.