# CVE-2026-106448: StableLib: Prototype poisoning via `__proto__` map keys in CBOR decoding

> Attackers can poison object prototypes via CBOR decoding to inject malicious properties, potentially bypassing security checks in downstream applications.

- **Severity:** High 8.9 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 Oct 2026
- **Updated:** 7 Oct 2026
- **Also known as:** GHSA-w48f-fwg7-ww6p

## What is CVE-2026-106448?

CVE-2026-106448 is a high-severity unsafe deserialization vulnerability in stablelib, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

StableLib is a stable library of useful TypeScript and JavaScript code. Prior to 2.0.4, the @stablelib/cbor CBOR map decoding path creates ordinary JavaScript objects and assigns attacker-controlled keys with bracket assignment. A map key named __proto__ invokes the inherited prototype setter instead of creating an ordinary own property, allowing the decoded object's prototype to contain attacker-controlled authorization or feature-flag values. Downstream code that trusts normal property lookup or merges the decoded object can therefore make security-sensitive decisions using inherited attacker data. This issue is fixed in version 2.0.4.

Weakness: CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-106448?

2 open source packages ship an affected version, including @stablelib/cbor.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@stablelib/cbor` | npm | All versions | 2.0.3 |
| `@stablelib/cbor` | npm | All versions | 2.0.3 |

## How do I fix CVE-2026-106448?

Upgrade @stablelib/cbor to 2.0.3 or later.

## Is CVE-2026-106448 being exploited?

There is no known exploitation of CVE-2026-106448 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-106448 and fix it if it is affected.

What it is: CVE-2026-106448 is a high-severity unsafe deserialization vulnerability in stablelib, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-106448 in the wild and no public exploit code.

Affected packages and fixed versions:
- @stablelib/cbor (npm): affected all versions; fixed in 2.0.3
- @stablelib/cbor (npm): affected all versions; fixed in 2.0.3

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-2026-106448/ (Markdown: https://insights.sbomify.com/CVE-2026-106448/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-106448
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-106448
- OSV: https://osv.dev/vulnerability/CVE-2026-106448

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-106448/
Summaries are generated and may contain mistakes; the official description above is the record.