CVE-2021-45958 is a medium-severity out-of-bounds write vulnerability in ujson (pip), affecting versions >= 1.34, < 5.2.0. It is fixed in 5.2.0.
UltraJSON (aka ujson) 1.34 through 5.1.0 has a stack-based buffer overflow in Buffer_AppendIndentUnchecked (called from encode).
A write operation targets a memory location beyond the intended buffer boundary. Typical impact: memory corruption, crash, or arbitrary code execution.
CVE-2021-45958 has a CVSS score of 5.5 (Medium). The vector is requires local access, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (5.2.0). Upgrading removes the vulnerable code path.
pip
ujson (>= 1.34, < 5.2.0)ujson → 5.2.0 (pip)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter instead of chasing every advisory.
Kodem's runtime-powered SCA identifies whether CVE-2021-45958 is reachable in your applications. Explore open-source security for your team.
See if CVE-2021-45958 is reachable in your applications. Get a demo
Upgrade ujson to 5.2.0 or later to resolve this vulnerability.
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2021-45958 is a medium-severity out-of-bounds write vulnerability in ujson (pip), affecting versions >= 1.34, < 5.2.0. It is fixed in 5.2.0. A write operation targets a memory location beyond the intended buffer boundary.
CVE-2021-45958 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
ujson (pip) versions >= 1.34, < 5.2.0 is affected.
Yes. CVE-2021-45958 is fixed in 5.2.0. Upgrade to this version or later.
Whether CVE-2021-45958 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade ujson to 5.2.0 or later.