CVE-2026-28481: OpenClaw Information Disclosure Flaw

CVE-2026-28481 Overview

OpenClaw versions 2026.1.30 and earlier contain an information disclosure vulnerability in the MS Teams attachment downloader extension. When enabled, the optional extension uses a permissive suffix-based allowlist for host validation. Upon receiving 401 or 403 HTTP responses during attachment downloads, the application automatically retries the request and sends Authorization bearer tokens to untrusted hosts that match the suffix-based allowlist pattern. This enables attackers controlling domains with matching suffixes to intercept and steal authentication tokens.

Critical Impact
Bearer token theft could allow attackers to impersonate users, access sensitive MS Teams data, and potentially pivot to other integrated services using the stolen credentials.

Affected Products

OpenClaw versions 2026.1.30 and earlier
OpenClaw MS Teams attachment downloader extension (when enabled)

Discovery Timeline

2026-03-05 - CVE CVE-2026-28481 published to NVD
2026-03-05 - Last updated in NVD database

Technical Details for CVE-2026-28481

Vulnerability Analysis

This vulnerability is classified under CWE-201 (Insertion of Sensitive Information Into Sent Data). The flaw exists in the MS Teams attachment downloader extension's retry logic for handling failed download attempts. When the downloader receives a 401 (Unauthorized) or 403 (Forbidden) response, it implements a retry mechanism that includes the Authorization bearer token in subsequent requests without properly validating whether the target host is authorized to receive sensitive authentication credentials.

The root issue stems from the allowlist implementation using suffix-based matching rather than strict domain validation. This approach means that any domain ending with an allowlisted suffix (such as microsoft.com) would be considered trusted, allowing malicious domains like attacker-microsoft.com to receive bearer tokens during retry attempts.

Root Cause

The vulnerability originates from insufficient validation in the host authorization logic for authentication retries. The isUrlAllowed function performs suffix-based matching against the configured allowHosts list, but this check was applied identically for both general URL access and authentication credential transmission. The lack of a separate, stricter authAllowHosts validation for bearer token transmission created the security gap.

Attack Vector

An attacker can exploit this vulnerability by:

Registering a domain that ends with an allowlisted suffix (e.g., evil-microsoft.com if microsoft.com is allowlisted)
Hosting a malicious endpoint that returns 401 or 403 responses to trigger the retry mechanism
Convincing a user to interact with a crafted MS Teams attachment link pointing to the attacker's domain
Capturing the bearer token sent during the authentication retry attempt

The attack requires user interaction to access a malicious attachment link and the MS Teams extension must be enabled.

typescript

// Security patch in extensions/msteams/src/attachments/download.ts
// Source: https://github.com/openclaw/openclaw/commit/41cc5bcd4f1d434ad1bbdfa55b56f25025ecbf6b

   isRecord,
   isUrlAllowed,
   normalizeContentType,
+  resolveAuthAllowedHosts,
   resolveAllowedHosts,
 } from "./shared.js";

The patch introduces a new resolveAuthAllowedHosts function to provide separate, stricter validation for hosts that are permitted to receive authentication credentials.

typescript

// Security patch in extensions/msteams/src/attachments/graph.ts
// Source: https://github.com/openclaw/openclaw/commit/41cc5bcd4f1d434ad1bbdfa55b56f25025ecbf6b

   tokenProvider?: MSTeamsAccessTokenProvider;
   maxBytes: number;
   allowHosts?: string[];
+  authAllowHosts?: string[];
   fetchFn?: typeof fetch;
   /** When true, embeds original filename in stored path for later extraction. */
   preserveFilenames?: boolean;

The fix adds a new authAllowHosts configuration parameter, separating general URL access permissions from authentication credential transmission permissions.

Detection Methods for CVE-2026-28481

Indicators of Compromise

Outbound HTTP requests containing Authorization headers to domains outside of known Microsoft infrastructure
Failed authentication attempts (401/403 responses) followed by retry requests to suspicious domains
Bearer tokens transmitted to non-Microsoft domains matching suffix patterns

Detection Strategies

Monitor network traffic for Authorization bearer tokens sent to non-standard Microsoft domains
Implement logging for MS Teams attachment download retry events and their target URLs
Alert on authentication retries where the retry target differs from the original request domain

Monitoring Recommendations

Enable verbose logging for the MS Teams attachment downloader extension
Review outbound connections from OpenClaw instances for unusual domain patterns
Audit the configured allowlist entries and validate they use strict domain matching

How to Mitigate CVE-2026-28481

Immediate Actions Required

Upgrade OpenClaw to version 2026.2.1 or later which contains the security fix
Review and restrict the MS Teams attachment downloader allowlist configuration
If upgrade is not immediately possible, consider temporarily disabling the MS Teams attachment downloader extension

Patch Information

The vulnerability has been patched in OpenClaw version 2026.2.1. The fix implements a separate authAllowHosts configuration that provides stricter validation specifically for bearer token transmission. Users should update to this version to receive the security fix. For detailed patch information, see the GitHub Security Advisory and the commit reference.

Workarounds

Disable the MS Teams attachment downloader extension if not required for operations
Implement network-level controls to block outbound bearer token transmission to non-Microsoft domains
Configure a restrictive authAllowHosts list after upgrading, limiting authentication credential transmission to strictly verified Microsoft endpoints

bash

# Configuration example - Restricting allowed hosts after patching
# In your OpenClaw configuration, specify strict auth-allowed hosts:
OPENCLAW_MSTEAMS_AUTH_ALLOW_HOSTS="graph.microsoft.com,teams.microsoft.com"
OPENCLAW_MSTEAMS_ALLOW_HOSTS="*.microsoft.com,*.microsoftonline.com"