CVE-2026-44978 Overview
CVE-2026-44978 is a heap out-of-bounds read vulnerability in xrdp, an open source Remote Desktop Protocol (RDP) server maintained by neutrinolabs. The flaw affects versions 0.10.6 and prior within the FIPS-specific receive paths. The default xrdp configuration is not affected. Exploitation requires the server to run with security_layer=negotiate or security_layer=rdp combined with crypt_level=fips in xrdp.ini. An unauthenticated remote attacker can send a crafted FIPS-protected Protocol Data Unit (PDU) to trigger the read, crashing the worker process. The issue is tracked under [CWE-20] (Improper Input Validation) and was fixed in version 0.10.6.1.
Critical Impact
Unauthenticated attackers can crash xrdp worker processes over the network when FIPS mode is enabled, causing localized denial of service against individual RDP sessions.
Affected Products
- neutrinolabs xrdp versions 0.10.6 and prior
- xrdp deployments configured with security_layer=negotiate or security_layer=rdp
- xrdp deployments configured with crypt_level=fips in xrdp.ini
Discovery Timeline
- 2026-07-20 - CVE-2026-44978 published to the National Vulnerability Database (NVD)
- 2026-07-22 - Last updated in NVD database
Technical Details for CVE-2026-44978
Vulnerability Analysis
The vulnerability resides in xrdp's FIPS-specific receive path, which processes inbound PDUs when Federal Information Processing Standards (FIPS) cryptography is enabled. The server reads a padding length field from attacker-controlled input and uses it in subsequent length arithmetic without validating its range. When the padding value exceeds the surrounding buffer size, xrdp performs a pointer underflow followed by a negative length calculation. The result is a heap out-of-bounds read that dereferences memory outside the intended buffer boundary. The read triggers a segmentation fault in the connection-handling process.
Root Cause
The root cause is missing input validation on the FIPS padding length field within the encrypted RDP payload. The FIPS receive routine trusts the padding descriptor supplied by the client and subtracts it from the received length without bounds checks. When the padding value is larger than the payload, the resulting length becomes negative and the data pointer underflows. This maps to [CWE-20] Improper Input Validation.
Attack Vector
The attack requires network reachability to the xrdp listener, typically TCP port 3389, and no authentication or user interaction. The attacker establishes an RDP session, negotiates the security layer, and delivers a malformed FIPS-protected PDU containing an oversized padding length. Because xrdp forks a dedicated process for each incoming connection, the crash terminates only the worker handling that session. The parent xrdp daemon continues accepting new connections, which limits the blast radius to per-session denial of service rather than a full service outage.
The vulnerability manifests only in FIPS-encrypted receive processing. See the GitHub Security Advisory GHSA-9cg5-f7m7-ppvj for the maintainer's technical description.
Detection Methods for CVE-2026-44978
Indicators of Compromise
- Repeated SIGSEGV or abnormal termination events for xrdp child processes shortly after inbound connections on port 3389.
- Core dumps produced by xrdp referencing FIPS decryption or padding-handling functions in the backtrace.
- xrdp session logs in /var/log/xrdp.log and /var/log/xrdp-sesman.log showing connections that terminate before authentication completes.
Detection Strategies
- Alert on repeated short-lived RDP connections from a single source IP that terminate before session establishment.
- Monitor for spikes in xrdp process crashes correlated with inbound traffic from untrusted networks.
- Inspect xrdp.ini across managed hosts to identify systems configured with crypt_level=fips combined with a negotiable or RDP security layer.
Monitoring Recommendations
- Forward xrdp logs and system journal entries to a centralized logging platform for correlation with network telemetry.
- Track process lifecycle events for the xrdp binary and flag abnormal exit codes from worker processes.
- Baseline normal RDP connection duration and alert on statistical anomalies indicating repeated pre-authentication crashes.
How to Mitigate CVE-2026-44978
Immediate Actions Required
- Upgrade xrdp to version 0.10.6.1 or later on all affected hosts.
- Inventory xrdp.ini configurations across the environment and identify systems using FIPS crypto with negotiable or RDP security layers.
- Restrict inbound access to TCP port 3389 at the network perimeter and permit only trusted management sources.
Patch Information
The maintainers released a fix in xrdp 0.10.6.1, available from the GitHub Release v0.10.6.1. The corresponding advisory is published as GitHub Security Advisory GHSA-9cg5-f7m7-ppvj. Administrators using distribution packages should track their vendor's backport for the fix.
Workarounds
- Revert crypt_level in xrdp.ini to a non-FIPS value such as high if operational and compliance requirements permit.
- Place xrdp behind a VPN or bastion host to eliminate direct exposure of the RDP listener to untrusted networks.
- Apply host-based firewall rules that limit RDP connections to known administrative subnets until the patched version can be deployed.
# Example: verify installed xrdp version and inspect security configuration
xrdp --version
grep -E '^(security_layer|crypt_level)' /etc/xrdp/xrdp.ini
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
