Answer in brief
CVE-2026-23455 records a Critical severity (CVSS 9.1) vulnerability in netfilter: nf_conntrack_h323: check for zero length in DecodeQ931(). The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
Answer in brief
CVE-2026-23455 records a Critical severity (CVSS 9.1) vulnerability in netfilter: nf_conntrack_h323: check for zero length in DecodeQ931(). The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 9.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=5e35941d990123f155b02d5663e51a24f816b6f3 <2121f5fbe88daff0f1fc5bc47d359426c74b86b0 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <65fa92f79677858b14b9e4b7275f26639afe2710 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <495e97af9e7249ee02b72bb1d0848a6efc3700f4 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <f5e4f4e4cdb75ec36802059a94195a31f193da60 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <633e8f87dad32263f6a57dccdb873f042c062111 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <b652b05d51003ac074b912684f9ec7486231717b || >=5e35941d990123f155b02d5663e51a24f816b6f3 <f173d0f4c0f689173f8cdac79991043a4a89bf66 | 2121f5fbe88daff0f1fc5bc47d359426c74b86b0, 65fa92f79677858b14b9e4b7275f26639afe2710, 495e97af9e7249ee02b72bb1d0848a6efc3700f4, f5e4f4e4cdb75ec36802059a94195a31f193da60, 633e8f87dad32263f6a57dccdb873f042c062111, 9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8, b652b05d51003ac074b912684f9ec7486231717b, f173d0f4c0f689173f8cdac79991043a4a89bf66 |
| Linux/Linuxgeneric | 2.6.17 | Not reported |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
Published upstream
Apr 3, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Jul 14, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 14, 2026
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.
Quoted source text, attributed separately from HOL analysis.
CVSS is 9.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=5e35941d990123f155b02d5663e51a24f816b6f3 <2121f5fbe88daff0f1fc5bc47d359426c74b86b0 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <65fa92f79677858b14b9e4b7275f26639afe2710 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <495e97af9e7249ee02b72bb1d0848a6efc3700f4 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <f5e4f4e4cdb75ec36802059a94195a31f193da60 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <633e8f87dad32263f6a57dccdb873f042c062111 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8 || >=5e35941d990123f155b02d5663e51a24f816b6f3 <b652b05d51003ac074b912684f9ec7486231717b || >=5e35941d990123f155b02d5663e51a24f816b6f3 <f173d0f4c0f689173f8cdac79991043a4a89bf66 | 2121f5fbe88daff0f1fc5bc47d359426c74b86b0, 65fa92f79677858b14b9e4b7275f26639afe2710, 495e97af9e7249ee02b72bb1d0848a6efc3700f4, f5e4f4e4cdb75ec36802059a94195a31f193da60, 633e8f87dad32263f6a57dccdb873f042c062111, 9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8, b652b05d51003ac074b912684f9ec7486231717b, f173d0f4c0f689173f8cdac79991043a4a89bf66 |
| Linux/Linuxgeneric | 2.6.17 | Not reported |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
Published upstream
Apr 3, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Jul 14, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 14, 2026
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.
Quoted source text, attributed separately from HOL analysis.