GHSA-mvm6-f9r3-fgfx
AWS SDK for .NET: Improper escaping of special characters in CloudFront policy document construction
Blast Radius
AWSSDK.CloudFront.NETAWSSDK.Extensions.CloudFront.SignersReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Summary
This notification is related to the CloudFront signing utilities in the AWS SDK for .NET, which are used to generate Amazon CloudFront signed URLs and signed cookies. A defense-in-depth enhancement has been implemented to improve handling of special characters, such as double quotes and backslashes, in input values.
Impact
The CloudFront signing utilities build policy documents that define access restrictions for signed URLs and cookies. If an application passes unsanitized input containing special characters to these utilities, the resulting policy document may not reflect the application's intended access restrictions. While the SDK was functioning safely within the requirements of the shared responsibility model, additional safeguards have been added to support secure customer implementations. Applications that already follow AWS security best practices for input validation are not impacted.
Impacted versions:
- AWS SDK for .NET V3 (
AWSSDK.CloudFront): < 3.7.510.7 - AWS SDK for .NET V4 (
AWSSDK.Extensions.CloudFront.Signers): 4.0.0.0 - 4.0.0.25
Patches
On February 25th, 2026, an enhancement was made to the AWS SDK for .NET CloudFront signing utilities. The enhancement ensures that special characters in input values are correctly handled. We recommend upgrading to the latest version.
Workarounds
No workarounds are needed, but customers should ensure that your application is following security best practices:
- Implement proper input validation in your application code before passing values to CloudFront signing utilities
- Update to the latest AWS SDK release on a regular basis
- Follow AWS security best practices for SDK configuration
References
If there are any questions or comments about this advisory, contact AWS Security via our vulnerability reporting page or directly via email to [email protected]. Please do not create a public GitHub issue.
Acknowledgement
AWS SDK for .NET thanks the Amazon Inspector Security Research team for identifying this issue and working through the coordinated process together.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | AWSSDK.CloudFront | all versions | 3.7.510.7 |
| .NETNuGet | AWSSDK.Extensions.CloudFront.Signers | ≥ 4.0.0.0&&< 4.0.0.26 | 4.0.0.26 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for AWSSDK.CloudFront. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update AWSSDK.CloudFront to 3.7.510.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mvm6-f9r3-fgfx 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 pinpoints whether GHSA-mvm6-f9r3-fgfx is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-mvm6-f9r3-fgfx. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-mvm6-f9r3-fgfx in your dependencies?
O3 detects GHSA-mvm6-f9r3-fgfx across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.