CVE-2026-50568: Fission Path Traversal Vulnerability

CVE-2026-50568 Overview

CVE-2026-50568 is a path traversal vulnerability in Fission, an open-source Kubernetes-native serverless framework. The flaw exists in the SanitizeFilePath function in pkg/utils/utils.go in versions prior to 1.25.0. The function used strings.HasPrefix(path, safedir) to validate path containment, which performs a lexical string comparison rather than a directory boundary check. A tenant with control over a sibling directory whose name begins with the safe-directory prefix can induce reads or writes outside the intended directory. The issue is tracked under [CWE-41] and was patched in Fission version 1.25.0.

Critical Impact
Authenticated local tenants sharing the fetcher or builder volume can read or write files outside the intended safe directory by pre-creating sibling directories with matching name prefixes.

Affected Products

Fission versions prior to 1.25.0
Fission builder component (pkg/builder/builder.go)
Fission fetcher component (pkg/fetcher/fetcher.go)

Discovery Timeline

2026-06-10 - CVE-2026-50568 published to NVD
2026-06-10 - Last updated in NVD database

Technical Details for CVE-2026-50568

Vulnerability Analysis

The vulnerability stems from incorrect path containment validation in Fission's SanitizeFilePath utility. The function was intended to ensure that user-supplied paths remained inside a designated safe directory. Instead, it relied on strings.HasPrefix(path, safedir), which only compares characters lexically. A path such as /packages-extra/evil satisfies HasPrefix against /packages, even though /packages-extra is a sibling directory rather than a child of /packages. The check failed to enforce a path-separator boundary between the safe directory and the remainder of the path.

Root Cause

The root cause is a missing directory boundary enforcement in the prefix check. A correct implementation must verify that the resolved absolute path equals the safe directory or is followed immediately by a path separator. Without that constraint, any sibling directory whose name begins with the safe-directory string is treated as inside the safe directory, breaking the intended sandbox.

Attack Vector

Exploitation requires local access with low privileges, such as a tenant workload running in the same Kubernetes namespace that shares the fetcher or builder volume. The affected call sites include the builder's Clean handler at pkg/builder/builder.go:208 and the fetcher's Fetch and Upload handlers in pkg/fetcher/fetcher.go. An attacker who can pre-create or control a sibling directory under the shared volume can supply crafted paths to these handlers. The result is a read or write operation outside the intended safe directory, potentially affecting other tenants' artifacts or function packages.

No public proof-of-concept code is referenced in the advisory. See the GitHub Security Advisory GHSA-r5jh-q2mw-gcx4 and Pull Request #3445 for the patch details.

Detection Methods for CVE-2026-50568

Indicators of Compromise

Unexpected files appearing in sibling directories adjacent to Fission's packages, fetcher, or builder staging paths on shared volumes.
Fetcher or builder log entries referencing paths outside the configured safe directory but sharing its name prefix.
Unauthorized modifications to function package archives between deployment and execution.

Detection Strategies

Audit Fission builder and fetcher logs for path arguments that contain the safe-directory string followed by characters other than /.
Inventory running Fission deployments and compare reported versions against 1.25.0 to identify vulnerable installations.
Review Kubernetes audit logs for tenant pods that mount Fission shared volumes and perform file operations on unexpected sibling paths.

Monitoring Recommendations

Enable filesystem auditing (auditd or eBPF-based file monitoring) on nodes hosting the Fission fetcher and builder pods.
Track changes to the shared volume backing the fetcher and builder, alerting on directory creation events whose names begin with reserved prefixes.
Correlate function deployment events with file write activity in the fetcher volume to surface unexpected write locations.

How to Mitigate CVE-2026-50568

Immediate Actions Required

Upgrade Fission to version 1.25.0 or later, which replaces the lexical prefix check with proper directory boundary validation.
Restrict tenant ability to pre-create directories on volumes shared with the Fission fetcher and builder until the upgrade is complete.
Review existing fetcher and builder volume contents for unauthorized sibling directories matching safe-directory prefixes.

Patch Information

The fix is included in Fission Release v1.25.0. The corrective changes are tracked in Pull Request #3445 and Pull Request #3446. Full advisory details are available in GHSA-r5jh-q2mw-gcx4.

Workarounds

Isolate Fission fetcher and builder workloads onto dedicated nodes or volumes that are not shared with untrusted tenants.
Apply Kubernetes PodSecurity policies to prevent untrusted workloads from mounting the same volumes used by Fission components.
Use read-only mounts where possible and enforce strict filesystem permissions on the parent directory of the safe directory to block sibling directory creation.

bash

# Upgrade Fission via Helm to the patched release
helm repo update
helm upgrade --install fission fission-charts/fission-all \
  --namespace fission \
  --version 1.25.0

# Verify the deployed version
kubectl -n fission get deployment -o jsonpath='{.items[*].spec.template.spec.containers[*].image}'