---
id: CVE-2026-102758
title: >-
  The `_nx_secure_x509_asn1_tlv_block_parse()` function parses ASN.1 TLV
  (tag-length-value) blocks out of DER-encoded data
summary: >-
  The `_nx_secure_x509_asn1_tlv_block_parse()` function parses ASN.1 TLV
  (tag-length-value) blocks out of DER-encoded data. It is the primitive
  underneath all X.509 certificate parsing in NetX Secure, and therefore runs on
  certificates sup…
severity: none
cwe:
  - CWE-126
vendor: Eclipse Foundation
product: NetX Duo
affected:
  - netx_duo <= 6.5.1.202602
published: '2026-09-29'
updated: '2026-09-29'
sourceUpdated: '2026-09-29T18:17:13.047'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-102758'
references:
  - url: >-
      https://github.com/eclipse-threadx/netxduo/security/advisories/GHSA-f95g-xc4w-mrcr
    label: emo@eclipse.org
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-29T17:41:02.256Z'
---

## Overview

The `_nx_secure_x509_asn1_tlv_block_parse()` function parses ASN.1 TLV (tag-length-value) blocks out of DER-encoded data. It is the primitive underneath all X.509 certificate parsing in NetX Secure, and therefore runs on certificates supplied by a remote peer during the TLS handshake.



The function reads the one-byte ASN.1 tag from the caller's buffer *before* checking that the buffer holds at least one byte. When a caller passes a remaining length of zero, the guard correctly returns `NX_SECURE_X509_ASN1_LENGTH_TOO_LONG`, but the read has already happened one byte past the end of the buffer.



code:



nx_secure/src/nx_secure_x509_asn1_tlv_block_parse.c



```



UINT _nx_secure_x509_asn1_tlv_block_parse(const UCHAR *buffer, ULONG *buffer_length, USHORT *tlv_type,

                                          USHORT *tlv_tag_class, ULONG *tlv_length,
                                          const UCHAR **tlv_data, ULONG *header_length)


{



UINT   current_index;



USHORT current_tag;



ULONG  length;



ULONG  length_bytes;

    current_index = 0;
    current_tag = buffer[current_index];      /* <-- read before the bounds check */
    if (*buffer_length < 1)
    {
        return(NX_SECURE_X509_ASN1_LENGTH_TOO_LONG);
    }


```



The remainder of the function is correctly ordered. The multi-byte length path is guarded by `length_bytes > 4 || length_bytes > *buffer_length` before its read loop, the decoded value is checked against `length > *buffer_length`, and the second single-byte length read follows its own `*buffer_length < 1` guard. The tag read is the only load placed ahead of its check.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.