# CVE-2026-27607: RustFS's Missing Post Policy Validation leads to Arbitrary Object Write

> Attackers can bypass upload policy restrictions to write arbitrary objects, spoof content types, and exhaust storage in RustFS object storage systems.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Feb 2026
- **Updated:** 25 Feb 2026
- **Also known as:** GHSA-w5fh-f8xh-5x3p

## What is CVE-2026-27607?

CVE-2026-27607 is a high-severity missing authorization vulnerability in rustfs, published on 25 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

RustFS is a distributed object storage system built in Rust. In versions 1.0.0-alpha.56 through 1.0.0-alpha.82, RustFS does not validate policy conditions in presigned POST uploads (PostObject), allowing attackers to bypass content-length-range, starts-with, and Content-Type constraints. This enables unauthorized file uploads exceeding size limits, uploads to arbitrary object keys, and content-type spoofing, potentially leading to storage exhaustion, unauthorized data access, and security bypasses. Version 1.0.0-alpha.83 fixes the issue.

Weakness: CWE-863 (Incorrect Authorization), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-27607?

2 open source packages ship an affected version, including rustfs. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `rustfs` | crates.io | From 1.0.0-alpha.56 | 1.0.0-alpha.83 |
| `rustfs` | crates.io | From 1.0.0-alpha.56 | 1.0.0-alpha.83 |

Products: Rustfs Rustfs.

## How do I fix CVE-2026-27607?

Upgrade rustfs to 1.0.0-alpha.83 or later.

## Is CVE-2026-27607 being exploited?

There is no known exploitation of CVE-2026-27607 in the wild and no public exploit code.

Public exploit code:

- Missing post-policy validation in RustFS (github_poc): https://github.com/nikeee/CVE-2026-27607

## Other vulnerabilities in rustfs

- [CVE-2025-68926](https://insights.sbomify.com/CVE-2025-68926/): RustFS has a gRPC Hardcoded Token Authentication Bypass (critical 9.8)
- [CVE-2026-27822](https://insights.sbomify.com/CVE-2026-27822/): Rust has Critical Stored XSS in Preview Modal, leading to Administrative Account Takeover (critical 9.1)
- [CVE-2025-68705](https://insights.sbomify.com/CVE-2025-68705/): RustFS Path Traversal Vulnerability (high 8.8)
- [CVE-2026-40937](https://insights.sbomify.com/CVE-2026-40937/): RustFS: Missing admin authorization on notification target endpoints allows unauthenticated configuration of event webhooks (high 8.3)
- [CVE-2026-21862](https://insights.sbomify.com/CVE-2026-21862/): RustFS sourceIp bypass via spoofed X-Forwarded-For/Real-IP headers (high 7.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27607 and fix it if it is affected.

What it is: CVE-2026-27607 is a high-severity missing authorization vulnerability in rustfs, published on 25 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-27607 in the wild and no public exploit code.

Affected packages and fixed versions:
- rustfs (crates.io): affected from 1.0.0-alpha.56; fixed in 1.0.0-alpha.83
- rustfs (crates.io): affected from 1.0.0-alpha.56; fixed in 1.0.0-alpha.83

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-27607/ (Markdown: https://insights.sbomify.com/CVE-2026-27607/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27607
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27607
- OSV: https://osv.dev/vulnerability/CVE-2026-27607

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27607/
Summaries are generated and may contain mistakes; the official description above is the record.