CVE-2026-21897: CryptoLib Buffer Overflow Vulnerability

CVE-2026-21897 Overview

CVE-2026-21897 is an out-of-bounds write vulnerability in NASA's CryptoLib, a software-only solution implementing the CCSDS Space Data Link Security Protocol - Extended Procedures (SDLS-EP) to secure communications between spacecraft running the core Flight System (cFS) and ground stations. The vulnerability exists in the Crypto_Config_Add_Gvcid_Managed_Parameters function, which contains an off-by-one boundary check error that allows writing past the end of the gvcid_managed_parameters_array, potentially corrupting adjacent memory including the gvcid_counter variable.

Critical Impact

This out-of-bounds write vulnerability can corrupt critical counter variables used in parameter lookup and registration logic, potentially compromising the integrity of secure spacecraft-to-ground communications.

Affected Products

• CryptoLib versions prior to 1.4.3
• NASA core Flight System (cFS) deployments using vulnerable CryptoLib versions
• Spacecraft and ground station systems implementing SDLS-EP via CryptoLib

Discovery Timeline

• 2026-01-10 - CVE CVE-2026-21897 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2026-21897

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write) and stems from an improper boundary validation in the array indexing logic. The Crypto_Config_Add_Gvcid_Managed_Parameters function is responsible for managing Global Virtual Channel Identifier (GVCID) parameters used in the SDLS-EP protocol. The function maintains an array of managed parameters (gvcid_managed_parameters_array) with a maximum size defined by GVCID_MAN_PARAM_SIZE (250 entries) and a counter variable (gvcid_counter) to track the current number of entries.

The flawed boundary check only validates whether gvcid_counter > GVCID_MAN_PARAM_SIZE, which incorrectly permits writing to index 250 (the 251st entry). Since the array is zero-indexed with 250 elements (indices 0-249), writing to index 250 causes an out-of-bounds write that overwrites the gvcid_counter variable, which is located immediately after the array in memory.

Root Cause

The root cause is an off-by-one error in the boundary validation logic. The check should use >= instead of > to properly validate array bounds. The correct condition should be gvcid_counter >= GVCID_MAN_PARAM_SIZE to prevent writing beyond the last valid index (249). This classic programming error results in the gvcid_counter being overwritten with arbitrary data when the 251st entry is added, corrupting the counter with whatever value is written to that memory location.

Attack Vector

The vulnerability is exploitable over the network since CryptoLib processes incoming communications from remote sources. An attacker could craft malicious requests that trigger the addition of GVCID managed parameters up to and including the 251st entry. When this occurs, the gvcid_counter is overwritten, which can have cascading effects on the parameter lookup and registration logic that relies on this counter for array bounds and iteration. The corrupted counter could cause:

• Incorrect parameter lookups leading to security bypass
• Denial of service through infinite loops or invalid memory access
• Potential for further memory corruption depending on how the corrupted counter is used

The vulnerability mechanism involves an improper array bounds check in the Crypto_Config_Add_Gvcid_Managed_Parameters function. When processing GVCID parameters, the function validates the counter value but uses an incorrect comparison operator, allowing one extra entry beyond the array bounds. This causes the 251st parameter write to overflow into adjacent memory where gvcid_counter is stored. For complete technical details, refer to the GitHub Security Advisory GHSA-9x7j-gx23-7m5r.

Detection Methods for CVE-2026-21897

Indicators of Compromise

• Unexpected modifications to GVCID counter values during protocol operations
• Anomalous behavior in parameter lookup or registration operations
• Memory corruption errors or crashes in CryptoLib components
• Unusual network traffic patterns targeting GVCID parameter configuration endpoints

Detection Strategies

• Monitor for attempts to add more than 250 GVCID managed parameters in a single session
• Implement memory integrity monitoring for critical data structures in CryptoLib
• Deploy runtime application self-protection (RASP) to detect out-of-bounds write attempts
• Utilize AddressSanitizer or similar tools during testing to catch memory corruption issues

Monitoring Recommendations

• Enable verbose logging for Crypto_Config_Add_Gvcid_Managed_Parameters function calls
• Monitor spacecraft communication systems for unexpected protocol state changes
• Set up alerts for counter value anomalies that could indicate memory corruption
• Review system logs for crash reports or segmentation faults related to CryptoLib

How to Mitigate CVE-2026-21897

Immediate Actions Required

• Upgrade CryptoLib to version 1.4.3 or later immediately
• Audit deployed systems to identify all instances using vulnerable CryptoLib versions
• Review and verify the integrity of GVCID managed parameters configurations
• Implement network segmentation to limit exposure of vulnerable communication endpoints

Patch Information

NASA has released version 1.4.3 of CryptoLib which addresses this vulnerability. The fix corrects the boundary check in the Crypto_Config_Add_Gvcid_Managed_Parameters function to properly validate array bounds before writing. Organizations should download the patched version from the GitHub CryptoLib Release v1.4.3 and deploy it across all affected systems. The security advisory with full technical details is available at GitHub Security Advisory GHSA-9x7j-gx23-7m5r.

Workarounds

• Implement input validation at the application layer to reject requests that would exceed 250 GVCID parameters
• Add additional bounds checking wrapper functions around Crypto_Config_Add_Gvcid_Managed_Parameters
• Limit network access to systems running vulnerable CryptoLib versions until patching is complete
• Consider enabling compiler-level protections such as stack canaries and ASLR if not already active

The recommended mitigation approach involves updating the boundary check logic. Organizations unable to immediately upgrade should implement application-level controls to prevent the addition of more than 250 GVCID managed parameters. This can be accomplished by adding pre-validation checks before calling the vulnerable function. See the GitHub Security Advisory for implementation guidance.