# CVE-2026-39956: jq: Missing runtime type checks for _strindices lead to crash and limited memory disclosure

> Attackers can crash jq or read limited memory by exploiting missing type checks in the _strindices builtin when processing untrusted filters.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 13 Apr 2026
- **Updated:** 4 Sep 2026
- **Also known as:** ALPINE-CVE-2026-39956, AZL-82973, BELL-CVE-2026-39956, CLSA-2026-1786762772, CLSA-2026-1787781806, DEBIAN-CVE-2026-39956, ECHO-70de-e2dc-f745, GHSA-6gc3-3g9p-xx28

## What is CVE-2026-39956?

CVE-2026-39956 is a medium-severity memory corruption vulnerability in jqlang jq, published on 13 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

jq is a command-line JSON processor. Prior to version 1.8.2, 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, which is part of version 1.8.2.

Weakness: CWE-843 (Access of Resource Using Incompatible Type), CWE-476 (NULL Pointer Dereference), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-39956?

It affects 1 product.


Products: Jqlang Jq.

## How do I fix CVE-2026-39956?

Upgrade to a fixed version.

## Is CVE-2026-39956 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-39956 exists.

## Other vulnerabilities in jqlang jq

- [CVE-2026-32316](https://insights.sbomify.com/CVE-2026-32316/): jq: Integer overflow in jvp_string_append() allows Heap-based Buffer Overflow (high 8.2)
- [CVE-2024-53427](https://insights.sbomify.com/CVE-2024-53427/): Memory corruption in jq (high 8.1)
- [CVE-2025-48060](https://insights.sbomify.com/CVE-2025-48060/): AddressSanitizer: stack-buffer-overflow in jq_fuzz_execute (jv_string_vfmt) (high 7.7)
- [CVE-2023-49355](https://insights.sbomify.com/CVE-2023-49355/): Memory corruption in n/a (high 7.5)
- [CVE-2026-49839](https://insights.sbomify.com/CVE-2026-49839/): jq --rawfile invalid-state reuse after String too long causes heap-buffer-overflow (high 7.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-39956 and fix it if it is affected.

What it is: CVE-2026-39956 is a medium-severity memory corruption vulnerability in jqlang jq, published on 13 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-39956 exists.

Affected product: jqlang jq. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-39956/ (Markdown: https://insights.sbomify.com/CVE-2026-39956/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-39956
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-39956
- OSV: https://osv.dev/vulnerability/CVE-2026-39956

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-39956/
Summaries are generated and may contain mistakes; the official description above is the record.