CVE-2026-23455 remediation guide

Linux Linux, SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_h323: check for zero length in DecodeQ931() In DecodeQ931(), the UserUserIE code path reads a 16-bit length from the packet, then decrements it by 1 to skip the protocol discriminator byte before passing it to DecodeH323_UserInformation(). If the encoded length is 0, the decrement wraps to -1, which is then passed as a large value to the decoder, leading to an out-of-bounds read. Add a check to ensure len is positive after the decrement.

Open CVE record

ProductLinux Linux, SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP

Affected versions>= 5e35941d990123f155b02d5663e51a24f816b6f3 < 2121f5fbe88daff0f1fc5bc47d359426c74b86b0, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 65fa92f79677858b14b9e4b7275f26639afe2710, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 495e97af9e7249ee02b72bb1d0848a6efc3700f4, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < f5e4f4e4cdb75ec36802059a94195a31f193da60, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 633e8f87dad32263f6a57dccdb873f042c062111, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < b652b05d51003ac074b912684f9ec7486231717b, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < f173d0f4c0f689173f8cdac79991043a4a89bf66, >= 2.6.17, >= V3.1.6, >= V3.1.5, >= 2.6.17 < 5.10.253, >= 5.11 < 5.15.203, >= 5.16 < 6.1.167, >= 6.2 < 6.6.130, >= 6.7 < 6.12.78, >= 6.13 < 6.18.20, >= 6.19 < 6.19.10, 7.0

Fixed versions5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10

Priority basisReview · CVSS 9.1 · EPSS 1.34%

Identify the affected asset

Confirm whether Linux Linux, SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP is installed, record the deployed version and installation path, and identify exposed interfaces.

Record the product name, package or appliance identifier, and installed version.
Identify internet-facing, administrative, API, and internal access paths.
Preserve the pre-change configuration and relevant service logs.

Validate the affected-version match

Compare the deployed version with the affected range: >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 2121f5fbe88daff0f1fc5bc47d359426c74b86b0, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 65fa92f79677858b14b9e4b7275f26639afe2710, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 495e97af9e7249ee02b72bb1d0848a6efc3700f4, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < f5e4f4e4cdb75ec36802059a94195a31f193da60, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 633e8f87dad32263f6a57dccdb873f042c062111, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < 9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < b652b05d51003ac074b912684f9ec7486231717b, >= 5e35941d990123f155b02d5663e51a24f816b6f3 < f173d0f4c0f689173f8cdac79991043a4a89bf66, >= 2.6.17, >= V3.1.6, >= V3.1.5, >= 2.6.17 < 5.10.253, >= 5.11 < 5.15.203, >= 5.16 < 6.1.167, >= 6.2 < 6.6.130, >= 6.7 < 6.12.78, >= 6.13 < 6.18.20, >= 6.19 < 6.19.10, 7.0. Treat incomplete inventory results as unresolved.

Prioritize with independent signals

The CVSS severity warrants an early asset and exposure review. Combine this signal with asset criticality, exposure, compensating controls, and business impact.

Apply supported remediation

Follow the vendor advisory or supported update path. Current fixed-version status: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10. Preserve configuration and rollback material before change.

Verify the result

Confirm the resulting version, service health, authentication and access paths, monitoring coverage, and relevant security logs.

Confirm the expected version and package state.
Run a functional health check for critical service paths.
Review authentication, error, application, and security monitoring logs.
Reassess exposure if the supported fix cannot be applied.

Operational boundary

This page does not replace the vendor advisory, support contract, change-management process, or recovery plan. Do not infer that an asset is unaffected from an incomplete inventory query or a missing fixed-version field.