CVE-2026-53561: 
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CVE-2026-53561 is an improper authentication vulnerability in HiveServer2's SAML bearer-token validation in Apache Hive, allowing unauthenticated network attackers to authenticate as any arbitrary Hive user by sending a forged Authorization: Bearer token to the /cliservice HTTP endpoint. It affects Apache Hive versions 4.0.0 through 4.2.0 (and later unreleased branches) when deployed with HTTP transport and hive.server2.authentication=SAML. The vulnerability was published on August 25, 2026, with a patch released in version 4.2.1. It carries a CVSS v3.1 base score of 7.4 (High) (Github Advisory, Apache Hive Security Advisory).

The root cause is a logic inversion bug in the signatureMatches() method of HiveSamlAuthTokenGenerator.java, where MessageDigest.isEqual() was negated (!MessageDigest.isEqual(...)), causing the signature check to accept forged tokens and reject valid ones — effectively inverting the authentication gate (CWE-287, CWE-305, CWE-345). Additionally, the parse() method used split(SEPARATOR) without a limit, allowing crafted token payloads with embedded separators to manipulate key-value parsing, and the ThriftHttpServlet passed the raw (still Base64-encoded) token string to parse() rather than the decoded form. An attacker with network access to the HiveServer2 HTTP port can craft a Base64-encoded token string with an arbitrary username and any signature value, send it as an Authorization: Bearer header to /cliservice, and receive a fully authenticated session as the impersonated user — no credentials, SAML IdP interaction, or knowledge of the server signing secret required (Github Commit, Github Advisory).

A successful exploit grants an unauthenticated attacker a fully authenticated HiveServer2 session with the privileges of any impersonated Hive user, including high-value accounts such as administrators. This enables unauthorized query execution, exfiltration of data stored in Hive-managed tables (potentially including sensitive enterprise datasets in HDFS or cloud storage), and unauthorized data modification. Availability is not directly impacted, but the confidentiality and integrity of all data accessible to the impersonated user are fully compromised (Github Advisory, Feedly).

As of the time of disclosure, there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation (Feedly). The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.14–0.20%, placing it in a low exploitation probability tier in the near term. However, the attack requires no credentials and only network reachability to the HiveServer2 HTTP port, making it straightforward to exploit once the flaw is understood — the primary constraint (High attack complexity in CVSS) reflects the requirement that the target deployment must have SAML authentication enabled in HTTP mode (Github Advisory).

1. Reconnaissance: Identify Apache Hive deployments running versions 4.0.0–4.2.0 with HTTP transport enabled and hive.server2.authentication=SAML configured. Scan for exposed HiveServer2 HTTP ports (default 10001) using tools like Shodan, Censys, or nmap. Check for reverse proxies such as Apache Knox that may forward requests to HiveServer2.
2. Craft a forged token: Construct a token payload string in the format u=<target_username>;id=<arbitrary_id>;time=<current_epoch_ms>;rs=<arbitrary_relay_state>;sg=<any_bogus_signature>. Due to the inverted signatureMatches() logic, any non-matching signature will be accepted.
3. Base64-encode the token: Encode the crafted payload using standard Base64 encoding (e.g., echo -n 'u=admin;id=1;time=<ms>;rs=x;sg=bogus' | base64).
4. Send the forged request: Submit an HTTP POST request to the /cliservice endpoint with the header Authorization: Bearer <base64_encoded_token>, targeting the HiveServer2 HTTP port directly or through a Knox reverse proxy.
5. Obtain authenticated session: The server's flawed validation accepts the forged token, establishes an authenticated HiveServer2 session as the specified user, and returns a valid session handle for subsequent Thrift/JDBC operations (Github Commit, Github Advisory).

• Network: Unexpected or anomalous HTTP POST requests to /cliservice on the HiveServer2 HTTP port (default 10001) from unfamiliar source IPs; requests containing Authorization: Bearer headers from clients that have not completed a SAML SSO flow.
• Logs: HiveServer2 access logs showing successful authentication events (Successfully validated the token for user) for privileged or administrative users from unexpected source addresses or at unusual times; absence of corresponding SAML IdP authentication events for the same user/session.
• Logs: Thrift HTTP servlet logs recording sessions established without a preceding SAML callback/redirect flow; multiple rapid authentication attempts with different usernames from the same source IP.
• Process/Query Activity: Unexpected HiveQL queries (e.g., SHOW TABLES, SELECT *, EXPORT TABLE) executed under high-privilege user accounts, particularly from unfamiliar JDBC client identifiers or IP addresses.

The primary remediation is to upgrade Apache Hive to version 4.2.1, which contains the fix for HIVE-29653 addressing the inverted signature check, encoding issues, and token parsing flaw (Github Commit, Github Advisory). If an immediate upgrade is not feasible, the following workarounds can reduce exposure:

• Disable HTTP transport: Switch HiveServer2 to binary transport mode, which is not affected by this vulnerability.
• Switch authentication mode: Change hive.server2.authentication from SAML to KERBEROS or LDAP; deployments using Knox SSO with LDAP/Kerberos on the HiveServer2 side are not affected.
• Network restriction: Restrict access to the HiveServer2 HTTP port (typically 10001) to trusted networks only, and ensure reverse proxies such as Apache Knox perform SAML token validation before forwarding requests to HiveServer2.