CVE-2026-56369: ImageMagick AES-CTR Nonce Reuse Information Disclosure (Low Severity)

Technical summary

CVE-2026-56369 involves improper nonce management in ImageMagick's PasskeyEncipherImage function. AES-CTR (Advanced Encryption Standard in Counter mode) is a stream cipher that generates a keystream by encrypting sequential counter values with a block cipher. The security of AES-CTR depends critically on never reusing the same nonce with the same key—doing so allows an attacker to XOR two ciphertexts together to cancel out the keystream and recover plaintext. The vulnerability indicates that ImageMagick's implementation reuses nonces under certain conditions, potentially within the same image encryption session or across multiple encryptions with the same key. This violates CWE-323 (Reuse of Nonce, Key Pair in Encryption), a well-known cryptographic anti-pattern. Versions prior to 7.1.2-22 are affected.

Business impact

Organizations using ImageMagick to encrypt sensitive images—such as medical imaging systems, document management platforms, or content distribution services—face confidentiality breaches. An attacker with network access to encrypted images can extract the plaintext without the encryption key, violating data protection obligations. The impact is particularly severe in regulated industries (healthcare, finance) where image encryption is relied upon for HIPAA, PCI-DSS, or similar compliance. However, the attack requires the attacker to possess the encrypted images themselves and potentially knowledge of which images share encryption context, limiting the immediate threat surface in many deployments.

Affected systems

ImageMagick versions before 7.1.2-22 are vulnerable. ImageMagick is widely used in server-side image processing for web applications, content management systems, document conversion pipelines, and scientific imaging workflows. Any system that uses the PasskeyEncipherImage method to encrypt image data is at risk. Desktop and server installations across Linux, Windows, and macOS distributions are affected if running vulnerable versions.

Exploitability

Exploitability is limited by practical constraints. An attacker must: (1) obtain the encrypted images; (2) potentially have multiple encrypted images from the same encryption context to leverage nonce reuse; and (3) possess computational resources to perform XOR operations and cryptanalysis. There is no remote code execution, and the attack does not require authentication or user interaction. The CVSS score of 3.7 (LOW) reflects these factors—low attack vector complexity, but limited impact (confidentiality only) and the requirement to obtain ciphertexts. This is not an actively exploited vulnerability in the wild according to current threat intelligence.

Remediation

Upgrade ImageMagick to version 7.1.2-22 or later. The patched version addresses nonce reuse by ensuring that each encryption operation generates or uses a unique nonce. Organizations should verify that their ImageMagick installation explicitly uses the PasskeyEncipherImage method; if image encryption is not a feature in use, the practical risk is minimal. After patching, re-encrypt any sensitive images that may have been protected with vulnerable versions if the encryption keys have potentially been compromised or if images were accessible to untrusted parties.

Patch guidance

Apply the upgrade to ImageMagick 7.1.2-22 or later through your package manager or by downloading from the official ImageMagick repository. Verify the patch has been applied by checking the version string (convert -version or identify -version). Test the patched version in a non-production environment to ensure compatibility with your image processing workflows and dependent applications. Pay particular attention to custom scripts or applications that call PasskeyEncipherImage directly, and confirm they continue to function correctly post-patch.

Detection guidance

Monitor ImageMagick process execution and logging for version identification. If you maintain detailed logs of image encryption operations, review them for patterns consistent with nonce reuse (e.g., identical encryption parameters or timestamps in rapid succession with the same key material). Network-based detection is difficult; this vulnerability manifests as data loss (unauthorized plaintext recovery) rather than system intrusion. Conduct an inventory of all systems running ImageMagick, especially in image processing pipelines, and prioritize those that handle sensitive or regulated image data.

Why prioritize this

Although assigned a LOW CVSS score, this vulnerability should be prioritized in environments where ImageMagick's encryption features are actively used to protect sensitive images. The fact that it does not appear on the KEV catalog suggests limited active exploitation, but the cryptographic nature of the flaw means that any images encrypted with vulnerable versions remain at risk indefinitely—decryption can occur long after the attack. Organizations in regulated industries or those encrypting confidential imagery should treat this as higher priority than the CVSS score alone suggests.

Risk score, explained

The CVSS 3.1 score of 3.7 (LOW) reflects: Attack Vector = Network (images could be exfiltrated); Attack Complexity = High (attacker must obtain encrypted images and possess cryptanalytic capability); Privileges Required = None; User Interaction = None; Scope = Unchanged; Confidentiality Impact = Low (plaintext recovery is possible but depends on attacker effort); Integrity = None; Availability = None. The 'Low' rating is appropriate for a confidentiality-only cryptographic weakness without active exploitation, but it may underestimate risk in scenarios where encrypted images are high-value assets or compliance-critical.

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