CVE-2025-55199: Helm Package Manager DOS Vulnerability

CVE-2025-55199 Overview

CVE-2025-55199 is a denial-of-service vulnerability in Helm, the package manager for Kubernetes charts. Versions prior to 3.18.5 fail to safely process JSON Schema files that contain a $ref pointing to /dev/zero. When Helm loads such a schema, it consumes all available memory and terminates with an out-of-memory (OOM) error. The flaw is classified under [CWE-770: Allocation of Resources Without Limits or Throttling]. Exploitation requires a user to load a malicious chart, but no privileges or authentication are needed on the target system.

Critical Impact
A crafted Helm chart can force the Helm client or automation pipeline to exhaust host memory, disrupting CI/CD workflows and Kubernetes deployment operations.

Affected Products

Helm versions prior to 3.18.5
Kubernetes deployment pipelines that ingest untrusted Helm charts
CI/CD systems using vulnerable Helm binaries or libraries

Discovery Timeline

2025-08-14 - CVE-2025-55199 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-55199

Vulnerability Analysis

Helm validates chart values against a values.schema.json file using JSON Schema semantics. The schema parser resolves $ref pointers to load referenced schema fragments. Prior to version 3.18.5, the resolver treats file paths supplied in $ref as trusted local resources and reads their entire contents into memory. When a chart references a pseudo-device such as /dev/zero, the read never terminates and Helm allocates memory until the process is killed.

The flaw stems from unbounded resource consumption during schema dereferencing. The parser did not validate the target of $ref or impose a size cap on the resolved content. Any environment executing helm install, helm template, or helm lint against the malicious chart triggers the condition. Automated pipelines that pull charts from public repositories are the most exposed.

Root Cause

The root cause lies in the pkg/chartutil/jsonschema.go component, which previously used the github.com/xeipuuv/gojsonschema library. That library resolved $ref values without size or type checks. The fix replaces the library with github.com/santhosh-tekuri/jsonschema/v6, which handles reference resolution with stricter validation and bounded reads.

Attack Vector

An attacker publishes or distributes a Helm chart containing a values.schema.json file with a $ref entry pointing to /dev/zero or a similarly unbounded resource. When a victim runs a Helm command that loads the chart, the process allocates memory continuously and terminates. In shared CI/CD runners, this can affect adjacent workloads and stall deployments.

// Patch excerpt: pkg/chartutil/jsonschema.go
// Replaces gojsonschema with santhosh-tekuri/jsonschema/v6
import (
    "bytes"
    "errors"
    "fmt"
    "strings"

    "github.com/santhosh-tekuri/jsonschema/v6"

    "helm.sh/helm/v3/pkg/chart"
)

Source: Helm commit b78692c

Detection Methods for CVE-2025-55199

Indicators of Compromise

Helm processes terminating with OOM errors during chart install, template, or lint operations
values.schema.json files inside charts containing $ref values that reference /dev/zero, /dev/urandom, or other unbounded device paths
Kernel oom-killer log entries naming the helm binary
CI/CD job failures immediately after fetching a chart from an untrusted repository

Detection Strategies

Statically scan Helm chart archives for $ref values referencing local file paths or device files before ingestion
Monitor memory consumption of Helm processes and alert when resident set size grows beyond a defined threshold
Audit installed Helm binary versions across build agents and developer workstations to identify versions prior to 3.18.5

Monitoring Recommendations

Collect and centralize CI/CD runner system logs, including dmesg output, to surface OOM kills tied to Helm
Track Helm command exit codes and duration in build telemetry to detect anomalous terminations
Alert on newly added charts in internal registries that include values.schema.json files with external or device-path $ref values

How to Mitigate CVE-2025-55199

Immediate Actions Required

Upgrade all Helm client installations and library dependencies to version 3.18.5 or later
Inventory CI/CD pipelines, developer workstations, and Kubernetes tooling images that bundle Helm
Restrict chart sources to trusted, signed repositories until upgrades are complete
Review recently ingested charts for malicious $ref entries in schema files

Patch Information

The fix is delivered in Helm 3.18.5. The maintainers replaced the JSON Schema library with github.com/santhosh-tekuri/jsonschema/v6, which validates $ref targets and prevents unbounded reads. Details are documented in the GitHub Security Advisory GHSA-9h84-qmv7-982p and the Helm commit b78692c.

Workarounds

Inspect every chart prior to loading and reject any values.schema.json containing $ref pointers to /dev/zero or other device files
Run Helm inside sandboxed containers with strict memory limits to contain OOM conditions
Disable automated chart installation from untrusted or public repositories until patched Helm binaries are deployed

bash

# Verify installed Helm version and upgrade if below 3.18.5
helm version --short

# Scan chart archives for suspicious $ref entries before use
grep -R '"\$ref"' ./charts | grep -E '/dev/(zero|urandom|null|random)'