CVE-2026-4036

Executive Summary

CVE-2026-4036 is an SQL injection vulnerability (CWE-89) in the Sharing API component of Synology DiskStation Manager (DSM) affecting releases before 7.2.1-69057-10, 7.2.2-72806-7, and 7.3.2-86009-2. The flaw allows a remote, authenticated attacker to obtain arbitrary sharing files by injecting special elements into SQL commands processed by the Sharing API. With a CVSS 3.1 base score of 6.5 (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N), the primary impact is high-confidentiality loss of file data; there is no demonstrated integrity or availability impact and no public exploit or Nuclei template at time of writing.

Technical Analysis

The vulnerability class is unambiguous: improper neutralization of special elements used in an SQL command, i.e., classic SQL injection (CWE-89). The NVD description places the flaw specifically in the Sharing API of Synology DSM, which is the subsystem that manages file/folder sharing links and their associated access logic. The attack surface is therefore the Sharing API's HTTP(S) endpoint surface, reachable over the network.

The critical qualifier is remote authenticated users. Unlike the pre-authentication SQLi typically seen in edge appliances, this flaw requires a valid DSM session or account. In the CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N), PR:L confirms the low-privilege prerequisite, AC:L indicates no special conditions are needed to trigger it, and C:H indicates the consequence is arbitrary sharing-file disclosure. The absence of I:N/A:N means the description and vector provide no evidence of data modification, deletion, or denial of service — this is a read/confidentiality bug, not a destructive one.

Because the public description does not disclose the vulnerable parameter name, the specific SQL statement, the query construction method (string concatenation vs. improper escaping/parameterization), or the exact endpoint path within the Sharing API, this report deliberately does not name functions, parameters, or routes. What can be stated with confidence at the vulnerability-class level is the mechanism:

1. The Sharing API accepts client-supplied input that is used to build a SQL statement executed against the DSM backend database.
2. The input is not neutralized — special SQL metacharacters are passed through into the query.
3. An authenticated user can therefore alter the query's logic, causing it to return records (sharing-file metadata/content) that the caller is not entitled to.
4. The net effect — reflected in the C:H subscore — is disclosure of arbitrary sharing files, i.e., shared files beyond the attacker's authorized scope.

Insufficient technical detail is available in the supplied intelligence to identify the vulnerable parameter or the underlying schema; any statement beyond the above would be speculation.

Exploitation Scenarios

No public PoC, exploit code, or Nuclei template exists for CVE-2026-4036 (PoC_STATUS: None). The attack chain below is inferred from the vulnerability class (CWE-89) and the NVD description, not from observed exploit code. No specific function names, parameters, or paths are asserted because none are provided in the source data.

1. Reconnaissance / target identification. An attacker identifies an internet- or LAN-exposed Synology DSM instance running a vulnerable version (before 7.2.1-69057-10 / 7.2.2-72806-7 / 7.3.2-86009-2). DSM management interfaces commonly listen on 5000/5001 (HTTP/HTTPS) and are readily fingerprinted via Shodan dorks such as product:"Synology DiskStation Manager".

2. Prerequisite — authenticated foothold. The attacker must already hold a valid DSM account (PR:L). This could be a low-privileged account obtained through phishing, credential reuse, a leaked/shared account, or a separate initial-access vulnerability. Because PR:L is required, an unauthenticated internet scanning hit alone is not sufficient to exploit this CVE.

3. Triggering the flaw class. Once authenticated, the attacker crafts requests to the Sharing API that carry SQL metacharacters inside the input the API uses to construct its SQL query. Because the input is not neutralized, the metacharacters are interpreted as SQL syntax rather than data. The attacker manipulates query logic (e.g., tautology/union-style manipulation of the WHERE clause) so the backend returns sharing-file records the caller is not authorized to view.

4. Post-exploitation impact. The manipulated query returns data corresponding to arbitrary sharing files, which the attacker exfiltrates over the same API responses. This is consistent with the CVSS confidentiality-high (C:H) subscore. There is no evidence in the provided data of write, tamper, or destructive capability, so the outcome is data theft/unauthorized disclosure of shared-file content and metadata.

Important caveat: specific payload strings, parameter names, and endpoint paths are intentionally omitted. Writing them without source-data support would be fabrication.

Impact Assessment

• Confidentiality: High (C:H). The defining impact per the NVD description is acquisition of arbitrary sharing files that the authenticated attacker is not entitled to. This can expose intellectual property, customer data, contracts, HR records, and backup/archive content stored on the NAS.
• Integrity / Availability: None (I:N/A:N). The vulnerability, as described and scored, does not permit data modification or service disruption. This lowers the immediate blast radius relative to RCE-class bugs but does not reduce the severity of a data-disclosure event.
• Privilege context. Exploitation requires an authenticated, low-privileged session (PR:L). This raises the bar versus pre-auth bugs, but once any credential is held — or a low-priv account is created via other means — the flaw enables horizontal/vertical data access beyond authorization boundaries, effectively an authorization bypass via SQLi.
• Blast radius. Any organization exposing a vulnerable DSM Sharing API, internally or externally, with multi-tenant or shared folder usage is exposed. NAS devices are common repositories for sensitive enterprise data, making a single successful exploitation potentially high-impact from a data-loss and regulatory (GDPR/HIPAA/PCI) perspective.
• Threat landscape. No CISA KEV listing, no EPSS score, and no public exploit exist as of this report. Risk is currently latent but realistic for targeted actors who already hold credentials, or for insiders and red teams performing post-authentication data hunting.

Detection Guidance

Detection content below targets the vulnerability class (SQL injection against the DSM Sharing API). Because no vulnerable parameter names are published, the rules use SQL-injection metacharacter and phrase heuristics rather than a known payload. Tune to your DSM request paths and normal sharing-API traffic to reduce false positives.

Sigma Rule

title: Potential SQL Injection Against Synology DSM Sharing API
id: 7c9a1f42-2b6e-4d3a-9f10-8a4b1c6e4036
status: experimental
description: Detects SQL injection metacharacters in requests to the Synology DSM Sharing API, consistent with CVE-2026-4036.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-4036
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
detection:
  selection_path:
    cs-uri-stem|contains:
      - '/webapi/entry.cgi'
      - '/sharing'
  selection_sqli:
    cs-uri-query|contains:
      - 'UNION SELECT'
      - 'OR 1=1'
      - "' OR '"
      - 'SLEEP('
      - 'BENCHMARK('
      - '--'
      - '/*'
  condition: selection_path and selection_sqli
fields:
  - c-ip
  - cs-uri-stem
  - cs-uri-query
falsepositives:
  - Legitimate applications passing SQL-like text in share names (rare)
level: high
tags:
  - attack.t1190
  - cve.2026.4036

YARA Rule

rule CVE_2026_4036_Synology_DSM_Sharing_SQLi
{
    meta:
        description = "Detects SQL injection payload markers targeting Synology DSM Sharing API (CVE-2026-4036)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-4036"
        date = "2026-01-01"
        cve = "CVE-2026-4036"
    strings:
        $api1 = "webapi/entry.cgi" ascii nocase
        $api2 = "/sharing" ascii nocase
        $sqli1 = "UNION SELECT" ascii nocase
        $sqli2 = "OR 1=1" ascii nocase
        $sqli3 = "' OR '" ascii nocase
        $sqli4 = "SLEEP(" ascii nocase
        $sqli5 = "BENCHMARK(" ascii nocase
    condition:
        ($api1 or $api2) and any of ($sqli*)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-4036 Possible SQL Injection Against Synology DSM Sharing API"; flow:established,to_server; http.uri; content:"/webapi/entry.cgi"; http.uri; content:"sharing"; http.uri; pcre:"/(UNION[\s\+]+SELECT|OR[\s\+]+1=1|SLEEP\(|BENCHMARK\()/i"; reference:cve,2026-4036; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-4036; classtype:web-application-attack; sid:2026403601; rev:1;)

(Note: the URI substrings above are generic DSM web-API indicators, not vendor-confirmed vulnerable paths; adjust to your environment since the exact Sharing API route is not published.)

Elastic Detection

sequence by source.ip with maxspan=5m
  [ network where http.request.method in ("GET","POST")
      and http.request.path : "*/webapi/entry.cgi*" ]
  [ network where http.request.body.text contains "UNION SELECT"
      or url.query contains "OR 1=1"
      or url.query contains "SLEEP(" ]

Splunk SPL Query

index=web OR index=proxy sourcetype=access_combined OR sourcetype=bluecoat
| eval uri=coalesce(uri, url, cs_uri_stem)
| eval qs=coalesce(query, cs_uri_query, url)
| where (like(uri, "%sharing%") OR like(uri, "%webapi/entry.cgi%"))
| search (qs="*UNION*SELECT*" OR qs="*OR+1=1*" OR qs="*SLEEP(*" OR qs="*BENCHMARK(*" OR qs="*' OR '*")
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip, uri
| where count > 0
| convert ctime(first_seen) ctime(last_seen)

Wazuh OSSEC Rule

<group name="web,synology,sqli,">
  <rule id="100436" level="12">
    <if_sid>31100</if_sid>
    <id>^403$|^200$</id>
    <match>sharing|webapi/entry.cgi</match>
    <regex>(UNION\s+SELECT|OR\s+1=1|SLEEP\(|BENCHMARK\()</regex>
    <description>CVE-2026-4036: Possible SQL injection attempt against Synology DSM Sharing API</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_4036,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix URL, OSV package entry, or workaround is present in the supplied intelligence. The following reflects the version boundaries stated in the NVD description only.

1) Immediate mitigations

• Restrict network exposure of the DSM Sharing API: do not publish ports 5000/5001 (or custom DSM ports) to the internet. Place the NAS behind a VPN or zero-trust gateway.
• Enforce least privilege: audit DSM accounts and remove or downgrade unnecessary accounts. Since exploitation requires an authenticated user (PR:L), minimizing valid credentials directly reduces exposure.
• Enable DSM firewall rules and account lockout/auto-block to limit credential-stuffing paths to the PR:L prerequisite.
• Monitor and alert on anomalous Sharing API query patterns using the detection content above.

2) Patch / upgrade steps

• Upgrade DSM to a release at or above 7.2.1-69057-10, 7.2.2-72806-7, or 7.3.2-86009-2 as applicable to your branch. These are the version boundaries cited in the NVD description.
• Because tracked patch sources report no confirmation (confidence 0/4), verify the fixed build directly with Synology's official DSM security advisory/release notes before treating a device as remediated.

3) Long-term hardening

• Maintain a patch cadence for NAS firmware; subscribe to Synology security advisories.
• Segment backup/storage networks from user and internet-facing networks.
• Apply database-access least privilege on the DSM backend where configurable.
• Log and retain Sharing API access logs for retro-hunting of prior exploitation (data-disclosure bugs may have already been used silently).

References

• NVD — CVE-2026-4036: https://nvd.nist.gov/vuln/detail/CVE-2026-4036
• CWE-89 — Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection'): https://cwe.mitre.org/data/definitions/89.html
• FIRST EPSS — Not yet scored as of this report (no EPSS value fabricated): https://www.first.org/epss/
• CISA Known Exploited Vulnerabilities Catalog — CVE-2026-4036 not listed (KEV: NO): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Synology Security Advisory portal (verify fixed DSM build directory): https://www.synology.com/en-global/security/advisory

Threat actor / exploit-in-the-wild status: No CISA KEV listing, no public PoC, no exploit code, and no Nuclei template are associated with CVE-2026-4036 in the supplied intelligence. There is no evidence of active exploitation or named threat-actor campaigns. EPSS has not scored this CVE — no EPSS value is asserted here.