CLI jq Crash via Unchecked StrIndices: Runtime Failure & Ptr Read
CVE-2026-39956 Published on April 13, 2026
jq: Missing runtime type checks for _strindices lead to crash and limited memory disclosure
jq is a command-line JSON processor. In commits after 69785bf77f86e2ea1b4a20ca86775916889e91c9, the _strindices builtin in jq's src/builtin.c passes its arguments directly to jv_string_indexes() without verifying they are strings, and jv_string_indexes() in src/jv.c relies solely on assert() checks that are stripped in release builds compiled with -DNDEBUG. This allows an attacker to crash jq trivially with input like _strindices(0), and by crafting a numeric value whose IEEE-754 bit pattern maps to a chosen pointer, achieve a controlled pointer dereference and limited memory read/probe primitive. Any deployment that evaluates untrusted jq filters against a release build is vulnerable. This issue has been patched in commit fdf8ef0f0810e3d365cdd5160de43db46f57ed03.
Vulnerability Analysis
CVE-2026-39956 is exploitable with local system access, requires user interaction. This vulnerability is considered to have a low attack complexity. Public availability of a proof of concept (POC) exploit exists for CVE-2026-39956. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality, a small impact on integrity, and a high impact on availability.
Weakness Types
Out-of-bounds Read
The software reads data past the end, or before the beginning, of the intended buffer. Typically, this can allow attackers to read sensitive information from other memory locations or cause a crash. A crash can occur when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string. The expected sentinel might not be located in the out-of-bounds memory, causing excessive data to be read, leading to a segmentation fault or a buffer overflow. The software may modify an index or perform pointer arithmetic that references a memory location that is outside of the boundaries of the buffer. A subsequent read operation then produces undefined or unexpected results.
NULL Pointer Dereference
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions.
What is an Object Type Confusion Vulnerability?
The program allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.
CVE-2026-39956 has been classified to as an Object Type Confusion vulnerability or weakness.
Products Associated with CVE-2026-39956
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Affected Versions
jqlang jq Version >= 69785bf77f86e2ea1b4a20ca86775916889e91c9, < fdf8ef0f0810e3d365cdd5160de43db46f57ed03 is affected by CVE-2026-39956Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.