Description
UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Affected versions were found to improperly decode certain characters. JSON strings that contain escaped surrogate characters not part of a proper surrogate pair were decoded incorrectly. Besides corrupting strings, this allowed for potential key confusion and value overwriting in dictionaries. All users parsing JSON from untrusted sources are vulnerable. From version 5.4.0, UltraJSON decodes lone surrogates in the same way as the standard library's `json` module does, preserving them in the parsed output. Users are advised to upgrade. There are no known workarounds for this issue.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| ultrajson | ultrajson | < 5.4.0 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | ujson | 5.4.0-1 | — |
| Debian 13 | ujson | 5.4.0-1 | — |
| Debian 12 | ujson | 5.4.0-1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | pandas | No fix yet | — |
| Ubuntu 26.04 LTS | pandas | No fix yet | — |
| Ubuntu 25.10 | pandas | No fix yet | — |
| Ubuntu 24.04 LTS | pandas | No fix yet | — |
| Ubuntu 22.04 LTS | pandas +1 | No fix yet | — |
Show 8 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | pandas | No fix yet | — |
| Ubuntu 18.04 LTS | pandas +1 | No fix yet | — |
| Ubuntu 16.04 LTS | pandas +1 | No fix yet | — |
| Ubuntu 14.04 LTS | pandas | No fix yet | — |
| Ubuntu Pro 22.04 LTS | ujson | 5.1.0-1ubuntu0.1~esm1 | USN-6629-1 |
| Ubuntu Pro 20.04 LTS | ujson | 1.35-4ubuntu0.1+esm1 | USN-6629-3 |
| Ubuntu Pro 18.04 LTS | ujson | 1.35-2ubuntu0.1~esm1 | USN-6629-1 |
| Ubuntu Pro 16.04 LTS | ujson | 1.33-1ubuntu0.1~esm2 | USN-6629-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat OpenStack 16 | python-ujson +1 | 2.0.3-3.el8ost | RHSA-2022:8864, RHSA-2022:8850 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP4 | python-ujson | 1.35-150100.3.5.1 | SUSE-SU-2022:2673-1 |
| SLES 15 SP3 | python-ujson | 1.35-150100.3.5.1 | SUSE-SU-2022:2673-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | python-ujson | 5.10.0-1.5 | openSUSE-SU-2025:15107-1 |
| openSUSE Leap 15.4 | python-ujson | 1.35-150100.3.5.1 | SUSE-SU-2022:2673-1 |
| openSUSE Leap 15.3 | python-ujson | 1.35-150100.3.5.1 | SUSE-SU-2022:2673-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | py3-ujson | 5.4.0-r0 | — |
| Alpine v3.23 | py3-ujson | 5.4.0-r0 | — |
| Alpine v3.22 | py3-ujson | 5.4.0-r0 | — |
| Alpine v3.21 | py3-ujson | 5.4.0-r0 | — |
| Alpine v3.20 | py3-ujson | 5.4.0-r0 | — |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | py3-ujson | 5.4.0-r0 | — |
| Alpine v3.18 | py3-ujson | 5.4.0-r0 | — |
| Alpine v3.17 | py3-ujson | 5.4.0-r0 | — |
| Alpine v3.16 | py3-ujson | 5.4.0-r0 | — |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| PyPI | ujson | < 5.4.0 | 5.4.0 | GHSA-wpqr-jcpx-745r |
Advisories 7
- RHSA-2022:8850 Red Hat Security Advisory: Red Hat OpenStack Platform 16.2.4 (python-ujson) security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- USN-6629-1 ujson vulnerabilities Ubuntu Security Notices (USN) · Jun 25, 2026
- USN-6629-3 ujson vulnerabilities Ubuntu Security Notices (USN) · Apr 27, 2026
- SUSE-SU-2022:2673-1 Security update for python-ujson SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2025:15107-1 python311-ujson-5.10.0-1.5 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- RHSA-2022:8864 Red Hat Security Advisory: Red Hat OpenStack Platform 16.1.9 (python-ujson) security update Red Hat Security Advisories (RHSA) · Jan 14, 2026
- WID-SEC-2022-2265 Red Hat OpenStack: Mehrere Schwachstellen BSI CERT-Bund (WID) · May 18, 2025