How severe is CVE-2026-44660?

CVE-2026-44660 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-44660 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-44660?

CVE-2026-44660 affects Ultrajson Project Ultrajson. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-44660?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-44660 have an EU (EUVD) identifier?

Yes. CVE-2026-44660 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-32663.

When was CVE-2026-44660 published?

CVE-2026-44660 was published on 2026-05-27 and last updated on 2026-06-17.

CVE-2026-44660

CVE-2026-44660 is a high-severity vulnerability in Ultrajson Project Ultrajson with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-401.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 8.7
EPSS exploit prediction: 0% (35th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-32663
Weakness: CWE-401
Affected product: Ultrajson Project Ultrajson
Published: 2026-05-27
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-44660?: 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.
How severe is CVE-2026-44660?: CVE-2026-44660 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-44660 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-44660?: CVE-2026-44660 affects Ultrajson Project Ultrajson. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-44660?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-44660 have an EU (EUVD) identifier?: Yes. CVE-2026-44660 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-32663.
When was CVE-2026-44660 published?: CVE-2026-44660 was published on 2026-05-27 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:ultrajson_project:ultrajson:*:*:*:*:*:python:*:*

More vulnerabilities in Ultrajson Project Ultrajson

CVE-2026-32875 — High (CVSS 7.5): UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Versions 5.10 through…
CVE-2026-32874 — High (CVSS 7.5): UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Versions 5.4.0 through…
CVE-2022-31116 — High (CVSS 7.5): UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Affected versions were…
CVE-2026-54911 — Medium (CVSS 6.5): UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.13.0,…
CVE-2022-31117 — Medium (CVSS 5.9): UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. In versions prior to…
CVE-2021-45958 — Medium (CVSS 5.5): UltraJSON (aka ujson) through 5.1.0 has a stack-based buffer overflow in Buffer_AppendIndentUnchecked (called from…

All CVEs affecting Ultrajson Project Ultrajson →

Other CWE-401 (Missing Release of Memory after Effective Lifetime) vulnerabilities

CVE-2026-46289 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: lib/scatterlist: fix length calculations in…
CVE-2025-39948 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: ice: fix Rx page leak on multi-buffer frames The…
CVE-2025-21954 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: netmem: prevent TX of unreadable skbs Currently…
CVE-2024-57947 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_set_pipapo: fix initial map…
CVE-2024-56779 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: nfsd: fix nfs4_openowner leak when concurrent…
CVE-2024-36911 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: hv_netvsc: Don't free decrypted memory In CoCo…

Browse all CWE-401 (Missing Release of Memory after Effective Lifetime) vulnerabilities →