SB2026092110 - Multiple vulnerabilities in IBM Operator for Apache Flink
Published: September 21, 2026 Updated: September 30, 2026
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 8 vulnerabilities.
1) Improper validation of certificate with host mismatch (CVE-ID: CVE-2025-68161)
CWE-ID: CWE-297 - Improper Validation of Certificate with Host Mismatch
CVSSv4: 6.3 [CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:L/SA:N]
The vulnerability allows a remote attacker to perform MitM attack.
The vulnerability exists due to the Socket Appender does not perform TLS hostname verification of the peer certificate, even when the "verifyHostName" configuration attribute or the "log4j2.sslVerifyHostName" system property is set to true. A remote attacker can perform MitM attack and intercept or redirect the log traffic.
2) Improper Certificate Validation (CVE-ID: CVE-2026-34477)
CWE-ID: CWE-295 - Improper Certificate Validation
CVSSv4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to perform a man-in-the-middle attack.
The vulnerability exists due to improper certificate validation in the TLS hostname verification handling of the verifyHostName attribute in Log4j Core SSL configuration when establishing TLS connections for SMTP, Socket, or Syslog appenders. A remote attacker can present a certificate issued by a trusted certificate authority to perform a man-in-the-middle attack.
The issue occurs only when TLS is configured via a nested SSL configuration element, and it does not affect the HTTP appender.
3) Improper Output Neutralization for Logs (CVE-ID: CVE-2026-34478)
CWE-ID: CWE-117 - Improper Output Neutralization for Logs
CVSSv4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to inject arbitrary log entries.
The vulnerability exists due to improper neutralization of CRLF sequences in Rfc5424Layout when processing logged data with direct Rfc5424Layout configuration using TCP framing. A remote attacker can supply specially crafted input containing CRLF sequences to inject arbitrary log entries.
Only users of stream-based syslog services who configure Rfc5424Layout directly are affected. Users of the SyslogAppender are not affected.
4) Deserialization of Untrusted Data (CVE-ID: CVE-2026-54512)
CWE-ID: CWE-502 - Deserialization of Untrusted Data
CVSSv4: 9.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to instantiate arbitrary classes.
The vulnerability exists due to deserialization of untrusted data in DatabindContext._resolveAndValidateGeneric() and PolymorphicTypeValidator handling when processing polymorphic type identifiers with generic parameters during deserialization. A remote attacker can supply a specially crafted type identifier and JSON data to instantiate arbitrary classes.
Only applications that accept untrusted JSON and have polymorphic typing enabled while relying on a configured PolymorphicTypeValidator allow-list are affected.
5) Incomplete List of Disallowed Inputs (CVE-ID: CVE-2026-54513)
CWE-ID: CWE-184 - Incomplete List of Disallowed Inputs
CVSSv4: 9.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to instantiate non-allowlisted types.
The vulnerability exists due to incomplete list of disallowed inputs in BasicPolymorphicTypeValidator.Builder.allowIfSubTypeIsArray() when deserializing attacker-controlled JSON containing array subtypes. A remote attacker can supply a crafted array wrapper to instantiate non-allowlisted types.
The issue occurs because array types are allowlisted based only on whether the class is an array, without validating the array component type against the configured allowlist, and no further validator check occurs for elements when per-element type IDs are absent.
6) Server-Side Request Forgery (SSRF) (CVE-ID: CVE-2026-54514)
CWE-ID: CWE-918 - Server-Side Request Forgery (SSRF)
CVSSv4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to cause outbound DNS requests and disclose limited network information.
The vulnerability exists due to server-side request forgery in JDKFromStringDeserializer when deserializing untrusted JSON into a type containing an InetSocketAddress field. A remote attacker can supply a crafted hostname value to cause outbound DNS requests and disclose limited network information.
The DNS lookup occurs during readValue before application-level validation or explicit connection logic.
CWE-ID: CWE-915 - Improperly Controlled Modification of Dynamically-Determined Object Attributes
CVSSv4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to modify otherwise ignored object attributes.
The vulnerability exists due to improper control of dynamically determined object attributes in BeanDeserializerBase.createContextual() when processing case-insensitive deserialization with per-property @JsonIgnoreProperties exclusions. A remote attacker can send crafted JSON input to modify otherwise ignored object attributes.
Only applications that enable case-insensitive property matching and rely on per-property @JsonIgnoreProperties to keep a field unwritable are vulnerable.
8) Improper Encoding or Escaping of Output (CVE-ID: CVE-2026-34480)
CWE-ID: CWE-116 - Improper Encoding or Escaping of Output
CVSSv4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to cause log event loss.
The vulnerability exists due to improper output neutralization in XmlLayout when processing log messages or MDC values containing XML 1.0 forbidden characters. A remote attacker can supply crafted input containing forbidden characters to cause log event loss.
The impact depends on the StAX implementation in use: built-in JRE StAX may produce malformed XML that downstream parsers reject, while alternative implementations may throw an exception during the logging call so the event is delivered only to Log4j's internal status logger.
Remediation
Install update from vendor's website.