jqlang jq JSON Object Hash Table weak hash

Summaryinfo

A vulnerability classified as problematic was found in jqlang jq. Affected is an unknown function of the component JSON Object Hash Table Handler. Such manipulation leads to weak hash. This vulnerability is traded as CVE-2026-40164. The attack may be launched remotely. There is no exploit available. Applying a patch is advised to resolve this issue.

Detailsinfo

A vulnerability was found in jqlang jq (version unknown) and classified as problematic. Affected by this issue is an unknown function of the component JSON Object Hash Table Handler. The manipulation with an unknown input leads to a weak hash vulnerability. Using CWE to declare the problem leads to CWE-328. The product uses an algorithm that produces a digest (output value) that does not meet security expectations for a hash function that allows an adversary to reasonably determine the original input (preimage attack), find another input that can produce the same hash (2nd preimage attack), or find multiple inputs that evaluate to the same hash (birthday attack). Impacted is availability. CVE summarizes:

jq is a command-line JSON processor. Before commit 0c7d133c3c7e37c00b6d46b658a02244fdd3c784, jq used MurmurHash3 with a hardcoded, publicly visible seed (0x432A9843) for all JSON object hash table operations, which allowed an attacker to precompute key collisions offline. By supplying a crafted JSON object (~100 KB) where all keys hashed to the same bucket, hash table lookups degraded from O(1) to O(n), turning any jq expression into an O(n²) operation and causing significant CPU exhaustion. This affected common jq use cases such as CI/CD pipelines, web services, and data processing scripts, and was far more practical to exploit than existing heap overflow issues since it required only a small payload. This issue has been patched in commit 0c7d133c3c7e37c00b6d46b658a02244fdd3c784.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-40164 since 04/09/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1600.001.

Applying the patch 0c7d133c3c7e37c00b6d46b658a02244fdd3c784 is able to eliminate this problem. The bugfix is ready for download at github.com.

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Productinfo

Vendor

• jqlang

Name

• jq

License

• open-source

Website

• Product: https://github.com/jqlang/jq/

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