Apache NiFi: Missing Authorization of Restricted Permissions when Replacing Flow Contents

Apache NiFi enforces an extra authorization tier called *Restricted* on components that can execute code, touch the filesystem, or otherwise reach outside the dataflow sandbox — think ExecuteProcess, ExecuteScript, GetFile. In versions 1.12.0 through 2.9.0, the framework forgot to re-check Restricted status when a user replaced an entire Process Group. A principal with ordinary write access on a Process Group could swap in a flow definition containing Restricted processors and the framework would happily accept it, even though the same user could not have added those processors individually. Once instantiated, Restricted processors run with the NiFi service account's privileges — which on most deployments means access to every database, S3 bucket, Kafka topic, and SFTP credential NiFi holds.

Vendor severity of HIGH (7.5) is defensible but slightly generous given the PR:H requirement — the attacker must already hold authenticated write access. We're holding the verdict at HIGH because the blast radius offsets the friction: NiFi is canonically a credential-rich data orchestrator, and the escalation path goes from *trusted contributor* to *full code execution as the NiFi service principal*. That's a classic insider-privesc footgun, not a perimeter RCE.

Why this verdict

• Authentication required (PR:H) — this is a privilege-escalation primitive, not a perimeter break. Attackers need a valid NiFi account with at least Process Group write, which limits the attacker pool to insiders, contractors, and credential-theft victims. That eats roughly −1.5 off the vendor score versus an unauthenticated RCE.
• Role multiplier — NiFi as canonical data-pipeline orchestrator: in the typical deployment NiFi holds DB credentials, S3 access keys, Kafka SASL secrets, and SFTP creds. The Restricted-processor escalation grants RCE as the service principal, and from there *mass data egress* is one ExecuteStreamCommand away. Blast radius is tenant- to data-domain-scale, holding the floor at HIGH.
• Role multiplier — multi-team shared NiFi clusters (common at large enterprises) are the worst case: a low-trust dataflow author pivots to flows owned by adjacent teams. Outcome: cross-team credential theft inside one cluster.
• No KEV, no public PoC — keeps the verdict from being upgraded; weaponization is trivial but not yet observed.
• Custom authorizer deployments (Apache Ranger plugin, file-based authorizer with explicit Restricted policies) may already block the exploit chain. That nudges the effective score down for hardened shops but does not change the bucket — most shipped configs use the default authorizer.

Why not higher?

CRITICAL requires either unauthenticated reachability or fleet-scale blast radius on a universally deployed component. PR:H eliminates the unauthenticated path, NiFi is not ubiquitous like Exchange or vCenter, and there is no active exploitation or KEV listing. The chain ends at the NiFi service principal — meaningful, but not domain-wide.

Why not lower?

MEDIUM would require either narrow affected range, low-value blast radius, or strong inherent friction beyond authentication. None apply: the affected range covers ~14 years of releases (1.12.0–2.9.0), the blast radius reaches every secret NiFi holds, and authenticated *write* access is a common power-user level in multi-team data platforms — not an admin-only choke point.

1. Audit and tighten Process Group write policies — Inventory every principal with write access on every Process Group via the NiFi /policies API. Remove standing write from anyone who doesn't actively author flows; move occasional editors to just-in-time access. Deploy within 30 days per the noisgate mitigation SLA.
2. Enable an authorizer that enforces Restricted policies independently — Configure file-based or Ranger authorizer with explicit access restricted components policies separate from generic write. The framework patch removes the in-framework check; the authorizer is now the only line of defense — make sure it's actually enforcing. Deploy within 30 days.
3. Front NiFi with SSO + MFA, block direct password auth — Most attack paths to step 1 are credential reuse or phishing. Force PingFederate / Okta / Azure AD in front of NiFi with conditional-access MFA. Disable single-user provider in production. Deploy within 30 days.
4. Run NiFi as an unprivileged service account with egress filtering — Reduces step-4 blast radius even if the chain lands. NiFi JVM should not have outbound internet by default; allowlist only required downstream endpoints. Apply immediately as a defense-in-depth standard.
5. Enable NiFi audit logging into SIEM and alert on flow-replace API calls — Add a detection on POST /nifi-api/process-groups/*/flow-contents correlated with new Restricted component instantiation by a principal that doesn't hold the access restricted components policy. Deploy within 30 days.

Run on each NiFi node as the nifi service user (or any user with read access to the install directory). Invoke as ./check_nifi_44914.sh /opt/nifi/nifi-current. No elevated privileges required — just reads NOTICE / version metadata.

#!/usr/bin/env bash
# noisgate check for CVE-2026-44914 (Apache NiFi Restricted authz bypass)
# Usage: ./check_nifi_44914.sh <NIFI_HOME>
# Exit 0=PATCHED, 1=VULNERABLE, 2=UNKNOWN

set -u
NIFI_HOME="${1:-/opt/nifi/nifi-current}"

if [ ! -d "$NIFI_HOME" ]; then
  echo "UNKNOWN: NIFI_HOME '$NIFI_HOME' not found" >&2
  exit 2
fi

# Try to extract version from bootstrap or lib jars
VERSION=""
if [ -f "$NIFI_HOME/conf/bootstrap.conf" ]; then
  VERSION=$(grep -hoE 'nifi[-_]framework[-_]nar[-_][0-9]+\.[0-9]+\.[0-9]+' "$NIFI_HOME/lib/" 2>/dev/null | head -1 | grep -oE '[0-9]+\.[0-9]+\.[0-9]+')
fi

if [ -z "$VERSION" ]; then
  JAR=$(ls "$NIFI_HOME"/lib/nifi-framework-nar-*.nar 2>/dev/null | head -1)
  if [ -n "$JAR" ]; then
    VERSION=$(echo "$JAR" | grep -oE '[0-9]+\.[0-9]+\.[0-9]+')
  fi
fi

if [ -z "$VERSION" ]; then
  echo "UNKNOWN: could not determine NiFi version in $NIFI_HOME" >&2
  exit 2
fi

echo "Detected NiFi version: $VERSION"

# Semver compare: vulnerable if 1.12.0 <= version <= 2.9.0
IFS='.' read -r MAJ MIN PAT <<< "$VERSION"
ver_num=$((MAJ*1000000 + MIN*1000 + PAT))
low=$((1*1000000 + 12*1000 + 0))    # 1.12.0
high=$((2*1000000 + 9*1000 + 0))    # 2.9.0
fix=$((2*1000000 + 10*1000 + 0))    # 2.10.0 (fixed)

if [ "$ver_num" -ge "$low" ] && [ "$ver_num" -le "$high" ]; then
  echo "VULNERABLE: NiFi $VERSION is in affected range 1.12.0-2.9.0 for CVE-2026-44914"
  exit 1
elif [ "$ver_num" -ge "$fix" ]; then
  echo "PATCHED: NiFi $VERSION is at or above fix 2.10.0"
  exit 0
else
  echo "PATCHED: NiFi $VERSION predates affected range"
  exit 0
fi

Sources

1. Vulnerability-Lookup (CIRCL) — CVE-2026-44914
2. Cyberpress — Critical Apache NiFi Vulnerabilities Enable Authorization Bypass
3. GBHackers — Apache NiFi Vulnerabilities Expose Systems to Authorization Bypass
4. Cybersecurity News — Apache NiFi Authorization Bypass
5. Apache NiFi Security Reporting & Advisories
6. stack.watch — Apache NiFi Security Vulnerabilities 2026
7. CVE Details — Apache NiFi vulnerability list
8. Related CVE-2026-25903 mailing list announcement (sibling NiFi authz bug)