CVE-2026-27822: Rust has Critical Stored XSS in Preview Modal, leading to Administrative Account Takeover

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.4%, percentile 31: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 31% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes rustfs (crates.io (Rust)) < 1.0.0-alpha.83, fixed in 1.0.0-alpha.83. Check your lockfile, including transitive dependencies.

What it is

RustFS is a distributed object storage system built in Rust. Prior to version 1.0.0-alpha.83, a Stored Cross-Site Scripting (XSS) vulnerability in the RustFS Console allows an attacker to execute arbitrary JavaScript in the context of the management console. By bypassing the PDF preview logic, an attacker can steal administrator credentials from localStorage, leading to full account takeover and system compromise. Version 1.0.0-alpha.83 fixes the issue.

From the GitHub advisory

Summary A Stored Cross-Site Scripting (XSS) vulnerability in the RustFS Console allows an attacker to execute arbitrary JavaScript in the context of the management console. By bypassing the PDF preview logic, an attacker can steal administrator credentials from localStorage, leading to full account takeover and system compromise.

Details The vulnerability exists due to improper validation of the response content type during the file preview process and a lack of origin separation between the S3 object delivery and the management console.

1. Origin of Credentials: The RustFS Console stores highly sensitive S3 credentials (AccessKey, SecretKey, SessionToken) in the browser's localStorage. - File: console/composables/useAuth.ts - Evidence: Lines 14 and 18-25 show that credentials are held in useLocalStorage('auth.credentials', {}) and useLocalStorage('auth.permanent', undefined). 2. Insecure Preview Implementation: In console/components/object/preview-modal.vue, the application identifies a PDF file based on its extension or metadata and renders it using an . 3. Same-Origin Vulnerability: RustFS typically hosts the management console and the S3 API on the same origin (e.g., the same IP and port). 4. Bypass Attack: An attacker can upload a file named xss.pdf but set its Content-Type metadata to text/html. Because the iframe is hosted on the same origin as the console, the executed script has unrestricted access to the parent window's localStorage.

PoC

This PoC demonstrates how to steal a victim's administrative credentials by tricking them into previewing a malicious file.

Weakness type: CWE-79.

Product: rustfs (crates.io (Rust)) · Assigned by: GitHub_M · Published: 2026-02-25

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: required (a user must click/open something)
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.38% probability of exploitation activity in the next 30 days; percentile 31.

Timeline

• 2026-02-25 — CVE record last updated
• 2026-02-25 — CVE record published by GitHub_M
• 2026-02-25 — GitHub-reviewed advisory GHSA-v9fg-3cr2-277j published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-v9fg-3cr2-277j github.com
2. CVE.org record CVE-2026-27822 cve.org
3. NVD entry CVE-2026-27822 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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