CVE-2026-35044

BentoML: SSTI via Unsandboxed Jinja2 in Dockerfile Generation

An attacker who distributes a malicious bento archive can achieve arbitrary code execution on the host machine of any user who imports and containerizes the bento. This gives the attacker:

• Full access to the host filesystem (source code, credentials, SSH keys, cloud tokens)
• Ability to install backdoors or pivot to other systems
• Access to environment variables containing secrets (API keys, database credentials)
• Potential supply chain compromise if the victim's machine is a CI/CD runner

The attack is particularly dangerous because:

1. Users may reasonably expect bentoml containerize to be a safe build operation
2. The malicious template is embedded inside the bento archive and not visible without manual inspection
3. Execution happens on the host, not inside a Docker container, bypassing all isolation

CVE-2026-35044 has a CVSS score of 8.8 (High). The vector is network-reachable, 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 (1.4.38); upgrading removes the vulnerable code path.

Kodem intelligence

Replace the unsandboxed jinja2.Environment with jinja2.sandbox.SandboxedEnvironment and remove the dangerous jinja2.ext.do and jinja2.ext.debug extensions, which are unnecessary for Dockerfile template rendering.

In src/bentoml/_internal/container/generate.py, change lines 155-157:

# Before (VULNERABLE):
from jinja2 import Environment
# ...
ENVIRONMENT = Environment(
    extensions=["jinja2.ext.do", "jinja2.ext.loopcontrols", "jinja2.ext.debug"],
    trim_blocks=True,
    lstrip_blocks=True,
    loader=FileSystemLoader(TEMPLATES_PATH, followlinks=True),
)

# After (FIXED):
from jinja2.sandbox import SandboxedEnvironment
# ...
ENVIRONMENT = SandboxedEnvironment(
    extensions=["jinja2.ext.loopcontrols"],
    trim_blocks=True,
    lstrip_blocks=True,
    loader=FileSystemLoader(TEMPLATES_PATH, followlinks=True),
)

Additionally, review the second unsandboxed Environment in build_config.py:499-504 which also uses jinja2.ext.debug:

# build_config.py:499 - also fix:
env = jinja2.sandbox.SandboxedEnvironment(
    variable_start_string="<<",
    variable_end_string=">>",
    loader=jinja2.FileSystemLoader(os.path.dirname(__file__), followlinks=True),
)

1. What is CVE-2026-35044? CVE-2026-35044 is a high-severity security vulnerability in bentoml (pip), affecting versions <= 1.4.37. It is fixed in 1.4.38.
2. How severe is CVE-2026-35044? CVE-2026-35044 has a CVSS score of 8.8 (High). 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.
3. Which versions of bentoml are affected by CVE-2026-35044? bentoml (pip) versions <= 1.4.37 is affected.
4. Is there a fix for CVE-2026-35044? Yes. CVE-2026-35044 is fixed in 1.4.38. Upgrade to this version or later.
5. Is CVE-2026-35044 exploitable, and should I be worried? Whether CVE-2026-35044 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
6. What actually determines whether CVE-2026-35044 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.
7. How do I fix CVE-2026-35044? Upgrade bentoml to 1.4.38 or later.