jq CVE-2026-41256

Exploitation requires that a user explicitly invoke jq with the -f flag pointing to a filter file containing an embedded NUL byte. The attacker must be able to supply or place the crafted filter file on the target system in a location where the user or a script will execute it. Default jq behavior (reading filters from command-line arguments or stdin) does not trigger this vulnerability; the -f flag and file-based filter loading are necessary. The vulnerability does not affect filter programs passed directly as command-line arguments or piped to stdin, only those loaded from disk files via -f. No authentication is required, but user interaction is mandatory: someone must actively run the jq command with the malicious file. Systems using jq in automated pipelines with externally-sourced filter files, or interactive users who accept filter files from peers, are at heightened risk.

CVSS 5.5 (AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N) indicates local attack vector with low complexity and user interaction (opening a crafted filter file), resulting in high integrity impact but no confidentiality or availability loss. The local attack vector limits exposure to users who directly execute jq with untrusted filter files. However, the high integrity impact is significant: an attacker controlling the filter file can silently modify JSON transformations or inject logic that appears absent, potentially corrupting data pipelines or causing undetected data modification. The requirement for user interaction (UI:R) means this is not wormable; a user must explicitly run jq -f with an attacker-supplied file. No exploitation probability data (EPSS) or active exploitation status (KEV) provided, suggesting this is a recently discovered or low-visibility issue. The regression nature (breaking a prior fix) elevates concern for already-patched deployments. Real-world risk depends on whether jq is used in scripts that accept filter files from untrusted sources or whether security controls validate filter file integrity before execution.

An attacker crafts a malicious jq filter file named exploit.jq containing '. \x00 | input | del(.password)' where the first dot (.) is the intended legitimate filter but the second command (del(.password)) is hidden after the NUL byte. A user or administrator runs 'jq -f exploit.jq data.json' believing the filter will pass through JSON unchanged. The NUL byte causes jq to truncate and compile only the leading '.', appearing to process the file correctly, while the actual malicious code after the NUL is never executed, leaving the attacker's payload undetected within the file system.