CVE-2026-14612: FreeIPA ipa-otpd DoS Vulnerability

CVE-2026-14612 Overview

CVE-2026-14612 identifies two off-by-one errors in the FreeIPA ipa-otpd daemon's OAuth2 device authorization handler. The flaws occur when the handler processes oversized responses from a configured external OAuth2/OpenID Connect (OIDC) Identity Provider (IdP). An attacker who controls or performs a man-in-the-middle (MITM) attack against the IdP endpoint can trigger ipa-otpd to read or write one byte past the end of a fixed-size buffer. The vulnerability is classified under CWE-787 (Out-of-Bounds Write). Exploitation requires FreeIPA to be configured with an external IdP and a user to initiate the OAuth2 device authorization flow.

Critical Impact
The most likely outcome is a limited denial of service affecting the ipa-otpd daemon, disrupting OAuth2/OIDC-based authentication flows in FreeIPA deployments.

Affected Products

FreeIPA ipa-otpd daemon (deployments configured with external OAuth2/OIDC IdP)
Red Hat Identity Management components incorporating the vulnerable ipa-otpd code path
FreeIPA-based directory environments using OAuth2 device authorization

Discovery Timeline

2026-07-03 - CVE-2026-14612 published to NVD
2026-07-07 - Last updated in NVD database

Technical Details for CVE-2026-14612

Vulnerability Analysis

The defect resides in the OAuth2 device authorization handler within the FreeIPA ipa-otpd daemon. The handler parses responses returned from a configured external OAuth2/OIDC Identity Provider during the device authorization grant flow defined in RFC 8628. Two separate off-by-one errors exist in the code path that copies or indexes IdP response data into fixed-size stack or heap buffers. When the response exceeds the expected size, the handler either writes one byte beyond the buffer boundary or reads one byte past its allocated end. The scope is constrained to a single byte, which limits the practical impact to memory corruption sufficient to crash the daemon rather than enabling reliable code execution.

Root Cause

The root cause is incorrect boundary arithmetic in buffer length checks used when handling variable-length fields in OAuth2/OIDC IdP responses. Length calculations do not properly account for terminator bytes or index limits, allowing a single-byte overrun. This class of defect maps to CWE-787 (Out-of-Bounds Write) and includes an accompanying out-of-bounds read condition.

Attack Vector

Exploitation requires three preconditions: FreeIPA must be configured with an external OAuth2/OIDC IdP, the attacker must control or MITM that IdP endpoint, and a user must initiate the OAuth2 device authorization flow. An attacker meeting these conditions returns a crafted oversized response to the ipa-otpd daemon during the device authorization exchange. The daemon then performs the one-byte over-read or over-write, resulting in memory corruption and likely daemon termination. The high attack complexity reflects the requirement for MITM positioning and user interaction to trigger the flow.

Refer to the Red Hat CVE-2026-14612 advisory and Red Hat Bug Report #2496879 for vendor technical details.

Detection Methods for CVE-2026-14612

Indicators of Compromise

Unexpected crashes or restarts of the ipa-otpd daemon coinciding with OAuth2 device authorization attempts.
Core dumps or systemd service failure logs referencing ipa-otpd following IdP communication.
Anomalous TLS certificates or unexpected network hops between the FreeIPA server and the configured external IdP endpoint.
Malformed or oversized HTTP response bodies observed in captures of OAuth2/OIDC device authorization traffic.

Detection Strategies

Monitor journalctl -u ipa-otpd and /var/log/messages for repeated daemon termination, segmentation faults, or ASan-style diagnostics.
Inspect outbound HTTPS traffic from FreeIPA servers to the configured IdP for unexpected endpoints, certificate changes, or DNS anomalies indicative of MITM.
Correlate authentication failures for OAuth2/OIDC users with ipa-otpd service state transitions in centralized logging.

Monitoring Recommendations

Enable process crash reporting and forward ipa-otpd service events to a central SIEM.
Implement TLS certificate pinning or strict certificate authority validation for the IdP endpoint used by FreeIPA.
Alert on repeated OAuth2 device authorization failures originating from the same user session or client identifier.

How to Mitigate CVE-2026-14612

Immediate Actions Required

Apply vendor patches for FreeIPA ipa-otpd once available from your Linux distribution.
Audit FreeIPA configurations to identify servers using an external OAuth2/OIDC IdP for device authorization flows.
Verify that the configured IdP endpoint uses strict TLS validation and is reachable only over trusted network paths.
Restrict outbound network egress from FreeIPA servers to the specific IdP endpoints required for OAuth2 flows.

Patch Information

Refer to the Red Hat CVE-2026-14612 advisory and Red Hat Bug Report #2496879 for patch availability and updated ipa-otpd package versions. Track your distribution's FreeIPA security errata for backported fixes.

Workarounds

Temporarily disable the external OAuth2/OIDC IdP integration in FreeIPA if a patch is not yet available and the feature is not operationally required.
Enforce certificate pinning and mutual TLS between FreeIPA and the IdP endpoint to reduce MITM exposure.
Segment the FreeIPA server network path to the IdP so that only authenticated, trusted intermediaries can route the traffic.
Configure systemd to automatically restart ipa-otpd on failure to limit denial-of-service duration until a patch is deployed.

bash

# Example: ensure ipa-otpd auto-restarts on crash (mitigates DoS window)
# Review current unit configuration
systemctl cat ipa-otpd

# Add a drop-in to enforce restart-on-failure
sudo mkdir -p /etc/systemd/system/ipa-otpd.service.d
cat <<'EOF' | sudo tee /etc/systemd/system/ipa-otpd.service.d/restart.conf
[Service]
Restart=on-failure
RestartSec=2s
EOF

sudo systemctl daemon-reload
sudo systemctl restart ipa-otpd