CVE-2021-21277 is a high-severity (CVSS 8.8) remote code execution vulnerability in angular-expressions. A fix is available for angular-expressions — see the affected versions and patch details below.
Angular Expressions - Remote Code Execution
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-21277 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
angular-expressionsnpmDescription
Impact
The vulnerability, reported by GoSecure Inc, allows Remote Code Execution, if you call expressions.compile(userControlledInput) where userControlledInput is text that comes from user input.
This time, the security of the package could be bypassed by using a more complex payload, using a .constructor.constructor technique.
- If running angular-expressions in the browser, an attacker could run any browser script when the application code calls expressions.compile(userControlledInput).
- If running angular-expressions on the server, an attacker could run any Javascript expression, thus gaining Remote Code Execution.
Patches
Users should upgrade to version 1.1.2 of angular-expressions
Workarounds
A temporary workaround might be either to :
- disable user-controlled input that will be fed into angular-expressions in your application
OR
- allow only following characters in the userControlledInput :
if (/^[|a-zA-Z.0-9 :"'+-?]+$/.test(userControlledInput)) {
var result = expressions.compile(userControlledInput);
}
else {
result = undefined;
}
References
Removal of angular-expression sandbox
For more information
If you have any questions or comments about this advisory:
- Open an issue in angular-expressions
- Email us
Credits
The issue was reported by Maxime Nadeau from GoSecure, Inc.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | angular-expressions | all versions | 1.1.2npm install angular-expressions@1.1.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for angular-expressions, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update angular-expressions to 1.1.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21277 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-21277 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-21277. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-21277 in your dependencies?
O3 Security finds CVE-2021-21277 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.