CVE-2026-55088 in Etherpad
Summary
by MITRE • 08/19/2026
Etherpad is a real-time collaborative editor. From 2.6.0 until 3.1.0, Etherpad's src/node/hooks/express/tokenTransfer.ts uses POST /tokenTransfer to store an author token for transfer between browsers and exposes it through GET /tokenTransfer/{uuid}. Although the record includes createdAt, the transfer has no expiration check, is not removed after successful redemption, and is returned by res.send(tokenData), including the raw author token. An unauthenticated attacker who obtains a transfer UUID can repeatedly redeem it, receive fresh author cookies, read the cleartext token, and impersonate the originating author for pad read and write operations. This issue is fixed in version 3.1.0.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified in Etherpad versions ranging from 2.6.0 to 3.1.0 represents a critical failure in session management and access control mechanisms within the application's token transfer functionality. The core of this issue resides in the src/node/hooks/express/tokenTransfer.ts module, which handles the POST /tokenTransfer endpoint for storing author tokens intended for cross-browser or cross-device transfers, as well as the GET /tokenTransfer/{uuid} endpoint used to retrieve these stored tokens. While the system records a creation timestamp via the createdAt field, it fundamentally lacks any logic to enforce an expiration policy on these transfer tokens. This absence of temporal constraints allows the tokens to remain valid indefinitely until they are manually deleted or the server state is reset, creating a persistent attack surface for unauthorized access attempts.
From a technical perspective, the flaw involves multiple layers of security negligence including improper resource cleanup and excessive information disclosure. Upon successful redemption of a transfer token, the system fails to remove the corresponding record from storage, allowing the same UUID to be redeemed repeatedly by an attacker. Furthermore, when retrieving data via GET /tokenTransfer/{uuid}, the server responds with res.send(tokenData), which includes the raw author token in cleartext rather than returning only a session identifier or performing secure authentication checks against the requesting client's existing credentials. This design choice exposes sensitive cryptographic material that is essential for maintaining user identity and permissions within the collaborative environment, effectively bypassing standard authentication barriers if an attacker can obtain the UUID associated with a valid transfer record.
The operational impact of this vulnerability is severe, as it enables unauthenticated attackers to impersonate legitimate users without needing their passwords or initial login credentials. By obtaining a transfer UUID through methods such as cross-site scripting attacks on shared pads, log file exposure, or other information leakage vectors, an attacker can repeatedly redeem the token to generate fresh author cookies. Once these cookies are acquired, the attacker gains full read and write access to the associated pad under the identity of the original author. This capability not only compromises data confidentiality by allowing unauthorized reading of sensitive documents but also undermines data integrity through malicious edits that appear to originate from a trusted user, potentially leading to social engineering attacks or corruption of collaborative content based on false attribution.
This vulnerability aligns with CWE-613, which describes insufficient session expiration, as the tokens do not expire after a reasonable period or single use. It also maps closely to CWE-200, an exposure of sensitive information to an unauthorized actor, due to the cleartext transmission of author tokens in API responses. In terms of offensive security frameworks, this behavior facilitates ATT&CK technique T1539, which involves stealing web session cookies, and can be leveraged for T1078, valid accounts, by allowing attackers to authenticate as existing users without proper credentials. The lack of idempotency in the redemption process further exacerbates the risk by enabling brute-force or replay attacks against the token transfer mechanism.
To mitigate this vulnerability, organizations running Etherpad must upgrade immediately to version 3.1.0 or later where these flaws have been addressed. For environments unable to patch instantly, administrators should implement network-level controls such as Web Application Firewalls that restrict access to the /tokenTransfer endpoints based on IP reputation and rate limiting to prevent repeated redemption attempts. Additionally, reviewing server logs for unusual patterns of token retrieval can help detect ongoing exploitation attempts. It is also advisable to audit any custom plugins or modifications to the express hooks module to ensure no similar insecure practices exist elsewhere in the codebase, particularly regarding how session data and authentication tokens are stored, transmitted, and invalidated after use.