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How CVE-2026-14681 Works
This vulnerability resides in PostgreSQL’s GSSAPI (Generic Security Services Application Program Interface) support, specifically within the authentication handshake process. When a client initiates a connection, PostgreSQL’s `ProcessStartupPacket()` function handles a sequence of negotiation messages for both SSL/TLS and GSSAPI. The flaw stems from improper enforcement of message integrity during this negotiation.
Under normal circumstances, a database administrator can configure `pg_hba.conf` to mandate GSSAPI authentication for specific connections. However, due to this vulnerability, a client can force the negotiation to deviate from these rules. By initiating a direct TLS connection, the client can manipulate the handshake to negotiate GSSAPI in a way that contradicts the `pg_hba.conf` settings.
The core issue is that even when `pg_hba.conf` appears to require GSSAPI, the connection may ultimately exchange data using TLS encryption alone. If the configured TLS settings are more permissive than the intended GSSAPI security policies, the connection continues with a lower level of protection than what the administrator intended. This allows an attacker to bypass the required GSSAPI authentication and potentially downgrade the security of the database connection.
The vulnerability affects PostgreSQL major versions 17 and 18, specifically minor versions before 17.11 and 18.5. Versions prior to PostgreSQL 17 are not impacted.
DailyCVE Form:
Platform: ……. PostgreSQL
Version: …….. 17.0-17.10, 18.0-18.4
Vulnerability :…… GSSAPI Integrity Bypass
Severity: ……. MEDIUM (CVSS: 4.2)
date: ………. 2026-08-13
Prediction: 2026-08-13
What Undercode Say:
The following commands can be used to check your PostgreSQL version and identify if you are running a vulnerable instance:
Check the PostgreSQL version postgres --version Or, if connected to the database, run: psql -c "SELECT version();" To check if GSSAPI is enabled in your configuration: grep -i "gss" /path/to/postgresql.conf grep -i "gss" /path/to/pg_hba.conf
Exploit: (Educational Purposes!)
This vulnerability is exploited by a malicious client during the initial connection handshake. The client initiates a TLS connection and then manipulates the GSSAPI negotiation messages within the `ProcessStartupPacket()` function. By alternating or crafting specific requests, the client can cause the server to accept a TLS-encrypted connection even when `pg_hba.conf` requires GSSAPI. This allows the client to bypass the intended authentication mechanism.
Protection:
To protect against CVE-2026-14681, you must upgrade your PostgreSQL installation to a patched version. The fixes are included in the following releases:
– PostgreSQL 17.11
– PostgreSQL 18.6 (Note: version 18.5 was skipped due to a regression)
Upgrading to these versions will correct the negotiation logic in `ProcessStartupPacket()` and ensure that GSSAPI authentication is properly enforced.
Impact:
If left unpatched, this vulnerability allows an attacker with network access to a PostgreSQL server to bypass GSSAPI authentication requirements. This can lead to a security downgrade where connections are secured only by TLS, potentially with more permissive settings than intended. The impact is limited to a partial loss of confidentiality and integrity, as reflected in the CVSS score. However, in environments where GSSAPI is a critical part of the security architecture, this bypass could undermine the entire authentication and encryption strategy.
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Sources:
Reported By: nvd.nist.gov
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