CVE-2023-48795

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Last Modified: UTC

Moderate Moderate Impact What does this mean?
5.9 CVSS v3 Base Score

Description

A flaw was found in the SSH channel integrity. By manipulating sequence numbers during the handshake, an attacker can remove the initial messages on the secure channel without causing a MAC failure. For example, an attacker could disable the ping extension and thus disable the new countermeasure in OpenSSH 9.5 against keystroke timing attacks.

Statement

This CVE is classified as moderate because the attack requires an active Man-in-the-Middle (MITM) who can intercept and modify the connection's traffic at the TCP/IP layer.

Although the attack is cryptographically innovative, its security impact is fortunately quite limited. It only allows the deletion of consecutive messages, and deleting most messages at this protocol stage prevents user authentication from proceeding, leading to a stalled connection.

The most significant identified impact is that it enables a MITM to delete the SSH2_MSG_EXT_INFO message sent before authentication begins. This allows the attacker to disable a subset of keystroke timing obfuscation features. However, there is no other observable impact on session secrecy or session integrity.

Mitigation

Update to the last version and check that client and server provide kex pseudo-algorithms indicating usage of the updated version of the protocol which is protected from the attack. If "kex-strict-c-v00@openssh.com" is provided by clients and "kex-strict-s-v00@openssh.com" is in the server's reply, no other steps are necessary.

Disabling ciphers if necessary:

If "kex-strict-c-v00@openssh.com" is not provided by clients or "kex-strict-s-v00@openssh.com" is absent in the server's reply, you can disable the following ciphers and HMACs as a workaround on RHEL-8 and RHEL-9:

1. chacha20-poly1305@openssh.com
2. hmac-sha2-512-etm@openssh.com
3. hmac-sha2-256-etm@openssh.com
4. hmac-sha1-etm@openssh.com
5. hmac-md5-etm@openssh.com

To do that through crypto-policies, one can apply a subpolicy with the following content:

cipher@SSH = -CHACHA20-POLY1305
ssh_etm = 0
e.g., by putting these lines into `/etc/crypto-policies/policies/modules/CVE-2023-48795.pmod`, applying the resulting subpolicy with `update-crypto-policies --set $(update-crypto-policies --show):CVE-2023-48795` and restarting openssh server.

One can verify that the changes are in effect by ensuring the ciphers listed above are missing from both `/etc/crypto-policies/back-ends/openssh.config` and `/etc/crypto-policies/back-ends/opensshserver.config`.

For more details on using crypto-policies, please refer to https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/html/security_hardening/using-the-system-wide-cryptographic-policies_security-hardening

Note that this procedure does limit the interoperability of the host and is only suggested as a temporary mitigation until the issue is fully resolved with an update.

For RHEL-7:
We can recommend to use strict MACs and Ciphers on RHEL7 in both files /etc/ssh/ssh_config and /etc/ssh/sshd_config.

Below strict set of Ciphers and MACs can be used as mitigation for RHEL 7.

Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
MACs umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512

- For Openshift Container Platform 4:
Please refer the KCS[1] document for verifying the fix in RHCOS.

[1] https://access.redhat.com/solutions/7071748

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2023-48795

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2023-48795

https://access.redhat.com/solutions/7071748

Content from terrapin-attack.com is not included.https://terrapin-attack.com/

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
EAP 8.0.1 apache-sshd Fixed RHSA-2024:1194
Migration Toolkit for Containers rhmtc/openshift-migration-velero-rhel8 Will not fix
OADP-1.3-RHEL-9 oadp/oadp-velero-rhel9 Fixed RHSA-2024:1859
OCP-Tools-4.12-RHEL-8 jenkins Fixed RHSA-2024:3635
OCP-Tools-4.12-RHEL-8 jenkins-2-plugins Fixed RHSA-2024:3635
OCP-Tools-4.13-RHEL-8 jenkins Fixed RHSA-2024:3636
OCP-Tools-4.13-RHEL-8 jenkins-2-plugins Fixed RHSA-2024:3636
OCP-Tools-4.14-RHEL-8 jenkins Fixed RHSA-2024:3634
OCP-Tools-4.14-RHEL-8 jenkins-2-plugins Fixed RHSA-2024:3634
OCP-Tools-4.15-RHEL-8 jenkins Fixed RHSA-2024:4597
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

Common Vulnerability Scoring System (CVSS) Score Details

Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authorities (CNA) source for its products and services (see Red Hat classifications ).

CVSS v3 Score Breakdown Red Hat NVD
CVSS v3 Base Score 5.9 5.9
Attack Vector Network Network
Attack Complexity High High
Privileges Required None None
User Interaction None None
Scope Unchanged Unchanged
Confidentiality Impact None None
Integrity Impact High High
Availability Impact None None

CVSS v3 Vector

Red Hat CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

NVD CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

 For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

What can I do if my product is listed as "Will not fix"?

 A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

 A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

 A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

I have a Red Hat product but it is not in the above list, is it affected?

 The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

 In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our This content is not included.Red Hat Vulnerability Scanner Certification program.

My product is listed as "Out of Support Scope". What does this mean?

 When a product is listed as "Out of Support Scope", it means a vulnerability with the impact level assigned to this CVE is no longer covered by its current support lifecycle phase. The product has been identified to contain the impacted component, but analysis to determine whether it is affected or not by this vulnerability was not performed. The product should be assumed to be affected. Customers are advised to apply any mitigation options documented on this page, consider removing or disabling the impacted component, or upgrade to a supported version of the product that has an update available.