--- title: "CVE-2023-41337\n | Ubuntu" description: Ubuntu is an open source software operating system that runs from the desktop, to the cloud, to all your internet connected things. url: https://ubuntu.com/security/CVE-2023-41337?format=md keywords: index, follow --- # CVE-2023-41337 Publication date 12 December 2023 Last updated 4 August 2025 --- Ubuntu priority **Medium** [Why this priority?](https://ubuntu.com/security/cves/about#priority ) ## Cvss 3 Severity Score **6.1 · Medium** [Score breakdown](https://ubuntu.com/security/CVE-2023-41337?format=md#impact-score) Toggle side navigation ## Description h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. In version 2.3.0-beta2 and prior, when h2o is configured to listen to multiple addresses or ports with each of them using different backend servers managed by multiple entities, a malicious backend entity that also has the opportunity to observe or inject packets exchanged between the client and h2o may misdirect HTTPS requests going to other backends and observe the contents of that HTTPS request being sent. The attack involves a victim client trying to resume a TLS connection and an attacker redirecting the packets to a different address or port than that intended by the client. The attacker must already have been configured by the administrator of h2o to act as a backend to one of the addresses or ports that the h2o instance listens to. Session IDs and tickets generated by h2o are not bound to information specific to the server address, port, or the X.509 certificate, and therefore it is possible for an attacker to force the victim connection to wrongfully resume against a different server address or port on which the same h2o instance is listening. Once a TLS session is misdirected to resume to a server address / port that is configured to use an attacker-controlled server as the backend, depending on the configuration, HTTPS requests from the victim client may be forwarded to the attacker's server. An H2O instance is vulnerable to this attack only if the instance is configured to listen to different addresses or ports using the listen directive at the host level and the instance is configured to connect to backend servers managed by multiple entities. A patch is available at commit 35760540337a47e5150da0f4a66a609fad2ef0ab. As a workaround, one may stop using using host-level listen directives in favor of global-level ones. ## Status Show unmaintained releases | Package | Ubuntu Release | Status | | --- | --- | --- | | h2o | 26.04 LTS resolute | Not in release | | 25.10 questing | Not in release | | 25.04 plucky | Ignored end of life, was needs-triage | | 24.10 oracular | Ignored end of life, was needs-triage | | 24.04 LTS noble | Needs evaluation | | 23.10 mantic | Ignored end of life, was needs-triage | | 23.04 lunar | Ignored end of life, was needs-triage | | 22.04 LTS jammy | Needs evaluation | | 20.04 LTS focal | Needs evaluation | | 18.04 LTS bionic | Needs evaluation | | 16.04 LTS xenial | Not in release | | 14.04 LTS trusty | Not in release | --- * [How can I get the fixes?](https://ubuntu.com/security/cves/about#security) * [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses) ## Severity score breakdown CVSS version: CVSS v3.0 **Base score** 6.1 · Medium * Base metrics | Parameter | Value | | --- | --- | | Attack vector | Adjacent | | Attack complexity | High | | Privileges required | Low | | User interaction | Required | | Scope | Unchanged | | Confidentiality impact | High | | Integrity impact | High | | Availability impact | None | * Scores | Parameter | Value | | --- | --- | | Base score | 6.1 · Medium | | Exploitability score | - | | Impact score | - | **Vector:** CVSS:3.1/AV:A/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:N ## References * [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-41337) * [NVD](https://nvd.nist.gov/vuln/detail/CVE-2023-41337) * [Launchpad](https://launchpad.net/bugs/cve/CVE-2023-41337) * [Debian](https://security-tracker.debian.org/tracker/CVE-2023-41337) ### Other references * *