phoenixframework phoenix up to 1.7.21/1.8.5 Elixir.Phoenix.Transports.LongPoll allocation of resources

Summaryinfo

A vulnerability has been found in phoenixframework phoenix up to 1.7.21/1.8.5 and classified as problematic. Affected by this issue is the function Elixir.Phoenix.Transports.LongPoll. The manipulation leads to allocation of resources. This vulnerability is referenced as CVE-2026-32689. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in phoenixframework phoenix up to 1.7.21/1.8.5 and classified as problematic. This issue affects the function Elixir.Phoenix.Transports.LongPoll. The manipulation with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Impacted is availability. The summary by CVE is:

Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix allows a denial of service via the long-poll transport's NDJSON body handling. In 'Elixir.Phoenix.Transports.LongPoll':publish/4, when a POST request is received with Content-Type: application/x-ndjson, the request body is split on newline characters using String.split/2 with no limit on the number of resulting segments. An attacker can send a body consisting entirely of newline bytes, causing a 1:1 amplification into a list of empty binaries — a 1 MB body produces approximately one million list elements, an 8 MB body approximately 8.4 million. Each element is then walked by Enum.map, materializing another list of the same size. This exhausts BEAM memory and schedulers, crashing the node and terminating all active sessions. A session token required to reach the vulnerable endpoint is freely obtainable by any client via an unauthenticated GET request to the same URL with a matching Origin header, making this attack effectively unauthenticated. This issue affects phoenix: from 1.7.0 before 1.7.22 and 1.8.6.

The weakness was published by Peter Ullrich as GHSA-628h-q48j-jr6q. It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-32689 since 03/13/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 1.7.22 or 1.8.6 eliminates this vulnerability. Applying the patch 1a67c61ff9ce0a7711662ac7354861917a7c80f7 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• phoenixframework

Name

• phoenix

Version

• 1.7.0
• 1.7.1
• 1.7.2
• 1.7.3
• 1.7.4
• 1.7.5
• 1.7.6
• 1.7.7
• 1.7.8
• 1.7.9
• 1.7.10
• 1.7.11
• 1.7.12
• 1.7.13
• 1.7.14
• 1.7.15
• 1.7.16
• 1.7.17
• 1.7.18
• 1.7.19
• 1.7.20
• 1.7.21
• 1.8.0
• 1.8.1
• 1.8.2
• 1.8.3
• 1.8.4
• 1.8.5

License

• open-source

Website

• Product: https://github.com/phoenixframework/phoenix/

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