# CVE-2026-44660: UltraJSON: Memory Leak in ujson.dump() on Write Failure > An attacker can cause memory exhaustion and denial of service by triggering write failures in ujson.dump(), affecting applications using the UltraJSON library. - **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 27 May 2026 - **Updated:** 30 May 2026 - **Also known as:** DEBIAN-CVE-2026-44660, ECHO-25c2-dc78-3aeb, GHSA-c38f-wx89-p2xg, MINI-m8jh-xqv7-hq36, PYSEC-2026-2293, SUSE-SU-2026:23114-1, SUSE-SU-2026:23136-1, SUSE-SU-2026:3539-1, UBUNTU-CVE-2026-44660, openSUSE-SU-2026:21518-1 ## What is CVE-2026-44660? CVE-2026-44660 is a high-severity denial of service vulnerability in ultrajson, published on 27 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1. Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime) ## Which versions are affected by CVE-2026-44660? 3 open source packages ship an affected version, including ujson. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `ujson` | PyPI | All versions | 5.12.1 | | `ujson` | PyPI | All versions | 5.12.1 | | `ujson` | PyPI | All versions | 5.12.1 | | `python-ujson` | SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise High Performance Computing 15 SP5-ESPOS | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise High Performance Computing 15 SP5-LTSS | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Module for Development Tools 15 SP7 | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Module for Package Hub 15 SP7 | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Server 15 SP4-LTSS | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Server 15 SP5-LTSS | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Server 15 SP6-LTSS | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Server 16.0 | All versions | 5.10.0-160000.3.1 | | `python-ujson` | SUSE:Linux Enterprise Server 16.0 | All versions | 5.10.0-160000.3.1 | | `python-ujson` | SUSE:Linux Enterprise Server for SAP Applications 15 SP4 | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Server for SAP Applications 15 SP5 | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Server for SAP Applications 15 SP6 | All versions | 1.35-150100.3.13.1 | | `python-ujson` | SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 5.10.0-160000.3.1 | | `python-ujson` | SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 5.10.0-160000.3.1 | | `python-ujson` | openSUSE:Leap 16.0 | All versions | 5.10.0-160000.3.1 | Products: Ultrajson Project Ultrajson. ## How do I fix CVE-2026-44660? Upgrade ujson to 5.12.1 or later. ## Is CVE-2026-44660 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44660 exists. ## Other vulnerabilities in ultrajson - [CVE-2026-32874](https://insights.sbomify.com/CVE-2026-32874/): UltraJSON has a Memory Leak parsing large integers allows DoS (high 7.5) - [CVE-2026-32875](https://insights.sbomify.com/CVE-2026-32875/): UltraJSON has an integer overflow handling large indent leads to buffer overflow or infinite loop (high 7.5) - [CVE-2026-54911](https://insights.sbomify.com/CVE-2026-54911/): UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps() (medium 6.5) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-44660 and fix it if it is affected. What it is: CVE-2026-44660 is a high-severity denial of service vulnerability in ultrajson, published on 27 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44660 exists. Affected packages and fixed versions: - ujson (PyPI): affected all versions; fixed in 5.12.1 - ujson (PyPI): affected all versions; fixed in 5.12.1 - ujson (PyPI): affected all versions; fixed in 5.12.1 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-2026-44660/ (Markdown: https://insights.sbomify.com/CVE-2026-44660/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44660 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44660 - OSV: https://osv.dev/vulnerability/CVE-2026-44660 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-44660/ Summaries are generated and may contain mistakes; the official description above is the record.