CVE-2026-79954: NASA CryptoLib Authentication Bypass Flaw

CVE-2026-79954 is an authentication bypass vulnerability in NASA CryptoLib 1.5.0 affecting the Telecommand receive path. Attackers can exploit improper SA verification to bypass authentication controls. This article covers technical details, affected versions, impact assessment, and mitigation strategies.

CVE-2026-79954 Overview

NASA CryptoLib 1.5.0 contains an authentication downgrade vulnerability in the Telecommand (TC) receive path. The receiver selects the Security Association (SA) used for Space Data Link Security (SDLS) processing solely from the Security Parameter Index (SPI) field inside the incoming frame. The implementation does not verify that the selected SA is authorized for the frame's Global Virtual Channel Identifier (GVCID). An attacker on the network path can supply a frame whose SPI points to a weaker SA, bypassing the integrity guarantees intended for that channel. The weakness is tracked under [CWE-306] (Missing Authentication for Critical Function).

Critical Impact
A network attacker can downgrade the SDLS security context on telecommand frames, injecting or modifying commands that would otherwise require authenticated processing.

Affected Products

NASA CryptoLib 1.5.0
Space Data Link Security (SDLS) telecommand receive path
Downstream ground-system or flight-software integrations using the affected library

Discovery Timeline

2026-09-18 - CVE-2026-79954 published to the National Vulnerability Database
2026-09-18 - Last updated in NVD database

Technical Details for CVE-2026-79954

Vulnerability Analysis

CryptoLib implements SDLS processing for CCSDS Telecommand frames used in spacecraft command and control. Each frame carries an SPI that identifies which Security Association the receiver should apply. The SA defines the cryptographic algorithms, keys, and authentication requirements for a given Virtual Channel.

In version 1.5.0, the receive path trusts the SPI value in the incoming frame without cross-checking that the referenced SA is bound to the frame's GVCID. As a result, an SA provisioned for a low-assurance channel can be applied to frames arriving on a channel that should require authenticated integrity. This breaks the isolation between channels and enables an authentication downgrade against telecommand traffic.

The vulnerability affects confidentiality and integrity guarantees for command traffic. Commands processed under an attacker-selected SA may be accepted despite missing or weaker authentication.

Root Cause

The root cause is missing authorization on SA selection. The lookup treats the SPI as an index into the SA table without validating that the SA is permitted for the arriving GVCID. This is a classic [CWE-306] pattern where a critical security decision is made using attacker-controllable input.

Attack Vector

Exploitation requires network access to the telecommand uplink or any intermediate path where an attacker can inject or modify TC frames. No authentication or user interaction is required. The attacker crafts a frame whose header targets a protected GVCID while its SPI references an SA with weaker authentication properties. The receiver applies the referenced SA and processes the frame under the downgraded security context.

See the Fluid Attacks Security Advisory and the GitHub Crypto Library Repository for technical details.

Detection Methods for CVE-2026-79954

Indicators of Compromise

TC frames whose SPI references an SA not provisioned for the frame's GVCID
Sudden appearance of frames processed under SAs associated with test or low-assurance channels on operational virtual channels
SDLS processing logs showing successful authentication using an SA that historically applies to a different GVCID

Detection Strategies

Instrument CryptoLib call sites to log the tuple of GVCID, SPI, and selected SA identifier for every processed TC frame
Compare observed GVCID-to-SA bindings against the authoritative SA provisioning table and alert on mismatches
Baseline expected SPIs per virtual channel and flag frames that deviate from the baseline

Monitoring Recommendations

Forward CryptoLib and ground-system telemetry to a centralized analytics platform for correlation across uplink sessions
Monitor frame acceptance rates per GVCID and alert on anomalies that correlate with unfamiliar SPI values
Retain TC frame metadata long enough to support retrospective analysis if a downgrade is later suspected

How to Mitigate CVE-2026-79954

Immediate Actions Required

Inventory all deployments of NASA CryptoLib 1.5.0 in ground and flight-adjacent systems
Restrict network paths that can inject TC frames to trusted operators and hardened links only
Audit the SA provisioning table and remove or disable SAs that are not required for current missions
Enable verbose logging on SDLS processing so GVCID-SPI-SA relationships are captured for review

Patch Information

No fixed version is listed in the NVD record at time of publication. Track the GitHub Crypto Library Repository for upstream commits that add GVCID-to-SA authorization checks, and consult the Fluid Attacks Security Advisory for the reporter's remediation guidance.

Workarounds

Apply a local patch that validates the selected SA's GVCID binding before SDLS processing continues
Enforce per-channel allowlists of permitted SPIs at an upstream frame filter
Provision only SAs with equivalent authentication strength for any GVCIDs that share an SA table, eliminating downgrade targets
Terminate TC uplinks over authenticated, integrity-protected transport to reduce opportunities for frame injection

bash

# Configuration example
# No vendor-published configuration mitigation is available.
# Refer to the Fluid Attacks advisory and the NASA CryptoLib repository for updates.