Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-23455 is a critical-severity Out-of-bounds Read (CWE-125) vulnerability in Linux Linux Kernel. Its CVSS base score is 9.1 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 30% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-8 (Security and Privacy Engineering Principles) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-23455 is an out-of-bounds read vulnerability in the Linux kernel's netfilter nf_conntrack_h323 subsystem, specifically within the DecodeQ931() function. The issue arises when processing the UserUserIE code path: the function reads a 16-bit length from the packet, decrements it by 1 to account for the protocol discriminator byte, and passes the result to DecodeH323_UserInformation(). If the encoded length is zero, the decrement causes an underflow to -1, interpreted as a large unsigned value, leading to an out-of-bounds read. It affects Linux kernel versions with the nf_conntrack_h323 module loaded for H.323 protocol connection tracking, with a CVSS v3.1 base score of 9.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H).
Remote, unauthenticated attackers can exploit this vulnerability over the network by sending crafted H.323 packets containing a zero-length UserUserIE field. No user interaction or privileges are required, and the attack has low complexity. Successful exploitation triggers the out-of-bounds read, potentially resulting in high-impact confidentiality loss through information disclosure or high-impact availability disruption, such as kernel crashes or denial of service.
Mitigation requires updating to a patched Linux kernel version. The fix adds a check in DecodeQ931() to ensure the length remains positive after decrementing, as implemented in stable kernel commits including https://git.kernel.org/stable/c/2121f5fbe88daff0f1fc5bc47d359426c74b86b0, https://git.kernel.org/stable/c/495e97af9e7249ee02b72bb1d0848a6efc3700f4, https://git.kernel.org/stable/c/633e8f87dad32263f6a57dccdb873f042c062111, https://git.kernel.org/stable/c/65fa92f79677858b14b9e4b7275f26639afe2710, and https://git.kernel.org/stable/c/9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-18711
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation directly finds out-of-bounds read flaws through static analysis, fuzzing, and dynamic bounds checks.
Secure engineering principles require bounds checking and memory-safe constructs that stop out-of-bounds reads from being introduced.
Process isolation confines the effects of an out-of-bounds read to the compromised process.
Input validation rejects malformed indices or lengths that would otherwise cause reads outside buffer bounds.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Vulnerability scanning and recording can discover instances of out-of-bounds reads after code is deployed.
Routine patching replaces vulnerable code containing out-of-bounds read flaws.
Secure-development practices such as bounds checking and memory-safe languages directly prevent out-of-bounds reads.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Logging can record evidence of an out-of-bounds read but does not prevent the weakness itself.
Secure development life cycle mandates input validation and bounds checking that directly prevent out-of-bounds reads.
Application security requirements include explicit bounds and memory-safety specifications that mitigate buffer over-reads.
Secure system architecture and engineering principles require memory-safe design patterns and runtime protections against out-of-bounds access.
Secure coding standards explicitly forbid unsafe pointer arithmetic and mandate bounds-checked reads, eliminating CWE-125.
Security testing in development and acceptance includes fuzzing and static analysis that detect out-of-bounds read defects before release.