CVE-2022-41862: Understanding PostgreSQL's Vulnerability in Establishing Kerberos Transport Encryption

In this long-read post, we will explore the details of the recently discovered vulnerability, CVE-2022-41862, in PostgreSQL. This vulnerability, if exploited, could potentially lead to the disclosure of sensitive information, as well as unintended error reports. For a comprehensive understanding of the subject matter, we will be discussing the underlying mechanism of this vulnerability, going through related code snippets, and providing original references for further study.

CVE-2022-41862 revolves around the establishment of Kerberos transport encryption in PostgreSQL. Specifically, a modified, unauthenticated server can send an unterminated string during this process. Under certain conditions, this server can cause a libpq client to over-read, subsequently reporting an error message containing uninitialized bytes.

Let's break down the key points of the vulnerability

1. It is related to PostgreSQL, a widely-used open-source relational database management system (RDBMS).

2. It occurs during the establishment of Kerberos transport encryption, a security protocol for securing network communication.

A malicious server sends an unterminated string during the process.

4. The server can cause the libpq client to over-read and report uninitialized bytes in the error message.

Before we dive into the code snippet highlighting the vulnerability, let's first understand the crucial terminologies and components.

Kerberos is a network authentication protocol designed to provide strong authentication for client-server applications. PostgreSQL supports using the GSSAPI (Generic Security Services Application Program Interface) security library to achieve secure communication via the Kerberos protocol.

Libpq is the default PostgreSQL client library, which is used by various PostgreSQL client applications, including the popular psql command-line tool.

Now let's examine the relevant code snippet that illustrates the vulnerability in action

/* File: fe-gssapi.c */
/* Function: pg_GSS_read_msg() */

static int
pg_GSS_read_msg(PGconn *conn, gss_buffer_desc *gbuf)
{
    uint32_t len;
    int ret;

    /* Step 1: Read the length of the incoming message */
    ret = pqsecure_read(conn, (char *) &len, 4);
    if (ret != 4)
        return ret;

    len = ntohl(len);

    /* Step 2: Allocate the memory for the message */
    gbuf->value = malloc(len);
    if (!gbuf->value)
    {
        /* Error: Insufficient memory */
        return -1;
    }

    /* Step 3: Read the actual message */
    ret = pqsecure_read(conn, gbuf->value, len);
    if (ret != (int) len)
    {
        /* Error: Failed to read the entire message */
        free(gbuf->value);
        return ret;
    }

    gbuf->length = len;
    return ;
}

In the code snippet, the pg_GSS_read_msg() function reads an incoming GSSAPI message from the server. The vulnerability arises when the server sends a message with an unterminated string. As the libpq client reads the message, it may over-read the uninitialized bytes, causing an error message to be reported containing sensitive information.

To further grasp the consequences of this vulnerability, you may refer to the following original references:

1. PostgreSQL CVE-2022-41862 Announcement
2. PostgreSQL Security Information
3. CVE-2022-41862 Details

In conclusion, we have touched on the details of CVE-2022-41862 in PostgreSQL, which involves the establishment of Kerberos transport encryption and a malicious server sending an unterminated string. As a result, the libpq client may over-read and inadvertently report uninitialized bytes in error messages. Understanding the nature of vulnerabilities like CVE-2022-41862 is essential to maintain the security and stability of an organization's PostgreSQL deployments. It highlights the importance of keeping software up-to-date and implementing robust security measures to protect sensitive information.

Timeline

Published on: 03/03/2023 16:15:00 UTC
Last modified on: 03/14/2023 15:17:00 UTC