GHSA-97rm-xj73-33jh — high GitHub Advisory (CVE-2026-27203) in npm/ebay-mcp

Description

The ebay_set_user_tokens tool allows updating the .env file with new tokens. The updateEnvFile function in src/auth/oauth.ts blindly appends or replaces values without validating them for newlines or quotes. This allows an attacker to inject arbitrary environment variables into the configuration file.

Impact

An attacker can inject arbitrary environment variables into the .env file. This could lead to:
- Configuration Overwrites: Attackers can overwrite critical settings like EBAY_REDIRECT_URI to hijack OAuth flows.
- Denial of Service: Injecting invalid configuration can prevent the server from starting.
- Potential RCE: In some environments, controlling environment variables (like NODE_OPTIONS) can lead to Remote Code Execution.

Found with MCPwner 🕶

Basic information

Type: reviewed
Severity: high
Advisory on GitHub: Open advisory ↗
Repository advisory: Open repository advisory ↗
Source code: Browse source ↗
Published (advisory): 2026-02-19 20:27:11 UTC
Updated: 2026-02-23 22:23:46 UTC
GitHub reviewed: 2026-02-19 20:27:11 UTC
NVD published: 2026-02-20

Score	Percentile
0.02%	4.46%

CVSS Scores

Base score	Version	Severity	Vector
8.3	3.1	—	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:L) Some sensitive info could get out, but not a total data dump. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.

Identifiers

Type	Value
GHSA	GHSA-97rm-xj73-33jh ↗
CVE	CVE-2026-27203 ↗

CWEs

CWE id	Name
CWE-15	External Control of System or Configuration Setting
CWE-74	Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

Credits

nedlir (reporter)

Affected packages (1)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem	Package	Vulnerable range	First patched	Vulnerable functions
npm	ebay-mcp	<= 1.7.2	—	—

eBay API MCP Server Affected by Environment Variable Injection