PatchTheCVECVE-2026-35209: defu is software that allows uers to assign default properties recursively
CVE-2026-35209 is a high-severity flaw (CVSS 7.5) affecting defu. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
defu is software that allows uers to assign default properties recursively. Prior to version 6.1.5, applications that pass unsanitized user input (e.g. parsed JSON request bodies, database records, or config files from untrusted sources) as the first argument to `defu()` are vulnerable to prototype pollution. A crafted payload containing a `__proto__` key can override intended default values in the merged resul. The internal `_defu` function used
Why this priority
- High severity
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 7.5 (High) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.4% (top 66%) |
| CISA exploited list | No |
| Weakness | CWE-1321 |
| Published | 2026-04-06 |
| Last modified | 2026-07-21 |
Last updated 2026-07-21 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-35209?
defu: upgrade to 6.1.5. Exact commands for each OS are on this page.
Is CVE-2026-35209 being exploited?
CVE-2026-35209 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-35209 affect?
CVE-2026-35209 affects defu. Severity is high (CVSS 7.5). defu is software that allows uers to assign default properties recursively. Prior to version 6.1.5, applications that pass unsanitized user input (e.g. parsed JSON request bodies, database records, or config files from untrusted sources) as
How urgent is CVE-2026-35209?
Priority 40/100. High severity; Remotely exploitable, no login, no user action