Validating Backup Integrity for Recovery Skill

Validating Backup Integrity for Recovery

When to Use

Use this skill when:

Verifying backup integrity before relying on backups for ransomware recovery
Building automated backup validation pipelines that run after each backup job
Auditing backup infrastructure to confirm recoverability for compliance (SOC 2, ISO 27001, NIST CSF RC.RP-03)
Detecting silent data corruption (bit rot) in backup storage before a disaster occurs
Validating that immutable or air-gapped backups have not been tampered with

Do not use for initial backup configuration or scheduling. This skill focuses on post-backup validation.

Prerequisites

Access to backup storage (local, NAS, S3, Azure Blob, GCS)
Python 3.9+ with hashlib (standard library)
Backup manifests or baseline hash files for comparison
Isolated restore environment for restore testing
Backup tool CLI access (restic, borgbackup, rclone, or vendor-specific)

Workflow

Step 1: Generate Baseline Hash Manifest

Create a cryptographic fingerprint of every file at backup time:

# Generate SHA-256 manifest for a directory
find /data/production -type f -exec sha256sum {} \; > /manifests/prod_baseline_$(date +%Y%m%d).sha256

# Verify manifest format
head -5 /manifests/prod_baseline_20260319.sha256
# e3b0c44298fc1c149afbf4c8996fb924...  /data/production/config.yaml
# a7ffc6f8bf1ed76651c14756a061d662...  /data/production/database.sql

Step 2: Verify Backup Archive Integrity

Check that the backup archive itself is not corrupted:

# Restic: verify backup repository integrity
restic -r s3:s3.amazonaws.com/backup-bucket check --read-data

# Borg: verify backup archive
borg check --verify-data /backup/repo::archive-2026-03-19

# Tar with gzip: verify archive integrity
gzip -t backup_20260319.tar.gz && echo "Archive OK" || echo "Archive CORRUPTED"

# AWS S3: verify object checksums
aws s3api head-object --bucket backup-bucket --key daily/2026-03-19.tar.gz \
  --checksum-mode ENABLED

Step 3: Perform Restore Test to Isolated Environment

# Restore to isolated test directory
restic -r s3:s3.amazonaws.com/backup-bucket restore latest --target /restore-test/

# Generate hash manifest of restored data
find /restore-test -type f -exec sha256sum {} \; > /manifests/restored_$(date +%Y%m%d).sha256

# Compare baseline and restored manifests
diff <(sort /manifests/prod_baseline_20260319.sha256) \
     <(sort /manifests/restored_20260319.sha256)

Step 4: Validate Data Completeness

# Count files in original vs restored
echo "Original: $(find /data/production -type f | wc -l) files"
echo "Restored: $(find /restore-test -type f | wc -l) files"

# Check total size
echo "Original: $(du -sh /data/production | cut -f1)"
echo "Restored: $(du -sh /restore-test | cut -f1)"

# Database consistency check after restore
pg_restore --list backup.dump | wc -l  # Count objects in dump
psql -c "SELECT schemaname, tablename FROM pg_tables WHERE schemaname='public';" restored_db

Step 5: Detect Ransomware Artifacts in Backups

Before trusting a backup for recovery, scan for ransomware indicators:

# Check for common ransomware file extensions
find /restore-test -type f \( \
  -name "*.encrypted" -o -name "*.locked" -o -name "*.crypt" \
  -o -name "*.ransom" -o -name "*.pay" -o -name "*.wncry" \
  -o -name "*.cerber" -o -name "*.locky" -o -name "*.zepto" \
\) -print

# Check for ransom notes
find /restore-test -type f \( \
  -name "README_TO_DECRYPT*" -o -name "HOW_TO_RECOVER*" \
  -o -name "DECRYPT_INSTRUCTIONS*" -o -name "HELP_DECRYPT*" \
\) -print

# Check file entropy (high entropy = possible encryption)
# Files with entropy > 7.9 out of 8.0 are likely encrypted
python agent.py --entropy-scan /restore-test

Step 6: Automate and Schedule Validation

# cron-based validation schedule
# Run nightly after backup window
0 4 * * * /opt/backup-validator/agent.py --validate-latest --notify-on-failure
# Weekly full restore test
0 6 * * 0 /opt/backup-validator/agent.py --full-restore-test --config /etc/backup-validator/config.json

Key Concepts

| Term | Definition | |------|-----------| | Hash Manifest | File containing cryptographic hashes (SHA-256) for every file in a dataset, used as integrity baseline | | Bit Rot | Gradual data corruption on storage media that silently alters file contents | | Immutable Backup | Backup that cannot be modified or deleted for a defined retention period | | Restore Test | Process of recovering data from backup to an isolated environment to verify recoverability | | File Entropy | Measure of randomness in file contents; encrypted files have entropy near 8.0 bits/byte | | 3-2-1 Rule | Keep 3 copies of data, on 2 different media types, with 1 offsite copy | | Backup Chain | Sequence of full and incremental backups that must all be intact for recovery |

Tools & Systems

| Tool | Purpose | |------|---------| | Restic | Encrypted, deduplicated backup with built-in integrity verification | | BorgBackup | Deduplicating backup with archive verification | | Rclone | Cloud storage sync with checksum verification | | AWS S3 Object Lock | Immutable backup storage with WORM compliance | | Azure Immutable Blob | Tamper-proof backup storage for compliance | | sha256sum | Standard hash computation for file integrity | | pg_restore | PostgreSQL backup validation and restore testing |

Common Pitfalls

Never testing restores: The most common failure mode. Backups that are never restored are untested assumptions.
Checking only archive integrity, not data integrity: A valid tar.gz can contain corrupted file contents. Always hash individual files.
Trusting last backup without scanning for ransomware: Backups may contain encrypted files if the infection predates the backup.
Ignoring incremental chain integrity: A single corrupted incremental backup can break the entire restore chain.
No alerting on validation failures: Backup validation must be monitored with alerts, not just logged silently.
Using MD5 for integrity: MD5 is cryptographically broken. Use SHA-256 or SHA-3 for integrity verification.

References

NIST SP 800-184: Guide for Cybersecurity Event Recovery
NIST CSF 2.0 RC.RP-03: Backup Integrity Verification
CIS Controls v8: Control 11 - Data Recovery
CISA Ransomware Guide: https://www.cisa.gov/stopransomware

Agent Skills: Validating Backup Integrity for Recovery

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