SUSE Rancher Manager cluster import manifest YAML injection via `authImage`

CVE-2026-44939 affects SUSE Rancher Manager cluster import manifests. SUSE says Rancher now validates the authImage parameter in cluster import manifests to prevent YAML injection. Fixed builds are v2.14.2, v2.13.6, v2.12.10, v2.11.14, and v2.10.12, which implies affected supported versions are the earlier releases on those branches. In practice, the weak point is the manifest-generation path used when registering/importing an existing Kubernetes cluster into Rancher.

There is no published CNA/NVD/MITRE CVSS baseline that I could find as of 2026-06-02, so this is a first-pass field assessment. The bug is real, but the vendor description overstates nothing and also leaves out the biggest real-world friction: this is not a spray-and-pray internet RCE. An attacker has to get into a cluster import workflow, influence the generated manifest, and then have that YAML applied by a privileged operator to a downstream cluster.

Why this verdict

• Requires a narrow attacker position: the attacker needs access to a live Rancher import/registration workflow, which usually implies prior compromise, insider access, or workflow-level social engineering.
• User interaction is part of the kill chain: the manifest has to be fetched and applied with kubectl, so a privileged operator or automation run is the trigger rather than a one-packet remote exploit.
• Impact is meaningful when it lands: YAML injection into an import manifest can translate into arbitrary Kubernetes object creation or manipulation in a high-value downstream cluster, often with elevated privileges.

Why not higher?

I do not see evidence of an unauthenticated, internet-wide exploit path, and I found no KEV listing, no public exploitation reporting, and no public PoC. The reachable population is narrower than generic Rancher exposure because this bug appears tied to a specific import-manifest workflow rather than the full management plane.

Why not lower?

This is not harmless parser weirdness. If the attacker can steer a victim into applying poisoned import YAML, the downstream cluster can be materially altered during a privileged admin operation, which is too much blast radius for LOW or IGNORE.

1. Restrict access to Rancher import workflows — Limit who can create, view, and use cluster registration/import tokens and URLs; treat them like privileged enrollment secrets. For a MEDIUM verdict there is no mitigation SLA, so keep this as standing hardening and go straight to patching within the 365-day remediation window.
2. Gate kubectl apply of import manifests through review — Make imported-cluster registration a platform-engineering-controlled change, not an ad hoc admin action. Require operators to review the fetched YAML or run it through a trusted wrapper before execution; for MEDIUM, there is no mitigation SLA, but this should remain in place until patched.
3. Log and alert on /v3/import/*.yaml access — Add reverse-proxy, Rancher audit, and CI/CD telemetry around import-manifest generation and consumption so you can spot unexpected token use, malformed parameters, or unusual registration bursts. For MEDIUM, there is no mitigation SLA, but this is worthwhile control-plane telemetry to maintain long term.
4. Harden downstream admission — Use Pod Security admission, Kyverno/Gatekeeper, image allowlists, and namespace/RBAC guardrails so a poisoned manifest has fewer useful payload options. This will not fix the bug, but it can collapse the most damaging post-apply outcomes while you work inside the 365-day remediation window.

Run this on an auditor workstation or a node with kubectl access to the management cluster where Rancher itself is installed. Invoke it as bash check-rancher-cve-2026-44939.sh cattle-system; it needs read access to the Rancher deployment/statefulset in that namespace and prints VULNERABLE, PATCHED, or UNKNOWN.

#!/usr/bin/env bash
# check-rancher-cve-2026-44939.sh
# Detects whether a Rancher Manager installation is on a fixed version for CVE-2026-44939.
# Exit codes:
#   0 = PATCHED
#   1 = VULNERABLE
#   2 = UNKNOWN / unable to determine

set -euo pipefail

NS="${1:-cattle-system}"

need() {
  command -v "$1" >/dev/null 2>&1 || { echo "UNKNOWN: missing required command '$1'"; exit 2; }
}

need kubectl
need awk
need sed

get_image() {
  kubectl -n "$NS" get deploy rancher -o jsonpath='{.spec.template.spec.containers[0].image}' 2>/dev/null && return 0
  kubectl -n "$NS" get statefulset rancher -o jsonpath='{.spec.template.spec.containers[0].image}' 2>/dev/null && return 0
  return 1
}

normalize_ver() {
  # Strip registry/name, leading v, and any suffix after the numeric semver core.
  # Examples:
  #   rancher/rancher:v2.14.2 -> 2.14.2
  #   v2.13.6 -> 2.13.6
  #   2.12.10-rc1 -> 2.12.10
  local raw="$1"
  raw="${raw##*:}"
  raw="${raw#v}"
  echo "$raw" | sed -E 's/^([0-9]+\.[0-9]+\.[0-9]+).*/\1/'
}

ver_to_int() {
  local v="$1"
  IFS='.' read -r major minor patch <<< "$v"
  printf '%03d%03d%03d\n' "$major" "$minor" "$patch"
}

cmp_ge() {
  local a b
  a=$(ver_to_int "$1")
  b=$(ver_to_int "$2")
  [[ "$a" -ge "$b" ]]
}

cmp_lt() {
  local a b
  a=$(ver_to_int "$1")
  b=$(ver_to_int "$2")
  [[ "$a" -lt "$b" ]]
}

IMAGE="$(get_image || true)"
if [[ -z "$IMAGE" ]]; then
  echo "UNKNOWN: could not find Rancher deployment/statefulset in namespace '$NS'"
  exit 2
fi

VER="$(normalize_ver "$IMAGE")"
if [[ ! "$VER" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
  echo "UNKNOWN: could not parse Rancher version from image '$IMAGE'"
  exit 2
fi

MAJOR_MINOR="$(echo "$VER" | awk -F. '{print $1"."$2}')"

case "$MAJOR_MINOR" in
  2.14)
    if cmp_ge "$VER" "2.14.2"; then
      echo "PATCHED: Rancher $VER (fixed in 2.14.2+)"
      exit 0
    else
      echo "VULNERABLE: Rancher $VER (affected 2.14.x < 2.14.2)"
      exit 1
    fi
    ;;
  2.13)
    if cmp_ge "$VER" "2.13.6"; then
      echo "PATCHED: Rancher $VER (fixed in 2.13.6+)"
      exit 0
    else
      echo "VULNERABLE: Rancher $VER (affected 2.13.x < 2.13.6)"
      exit 1
    fi
    ;;
  2.12)
    if cmp_ge "$VER" "2.12.10"; then
      echo "PATCHED: Rancher $VER (fixed in 2.12.10+)"
      exit 0
    else
      echo "VULNERABLE: Rancher $VER (affected 2.12.x < 2.12.10)"
      exit 1
    fi
    ;;
  2.11)
    if cmp_ge "$VER" "2.11.14"; then
      echo "PATCHED: Rancher $VER (fixed in 2.11.14+)"
      exit 0
    else
      echo "VULNERABLE: Rancher $VER (affected 2.11.x < 2.11.14)"
      exit 1
    fi
    ;;
  2.10)
    if cmp_ge "$VER" "2.10.12"; then
      echo "PATCHED: Rancher $VER (fixed in 2.10.12+)"
      exit 0
    else
      echo "VULNERABLE: Rancher $VER (affected 2.10.x < 2.10.12)"
      exit 1
    fi
    ;;
  *)
    echo "UNKNOWN: Rancher $VER is outside the publicly documented fixed branches for CVE-2026-44939"
    exit 2
    ;;
esac

Sources

1. SUSE Rancher Manager security advisories and CVEs
2. SUSE Rancher Manager v2.14.2 release notes
3. SUSE Rancher Manager v2.11.14 release notes
4. Rancher documentation: Registering Existing Clusters
5. Go package docs showing Rancher `auth-image` setting
6. CISA Known Exploited Vulnerabilities Catalog
7. FIRST EPSS project