# CVE-2026-47775: Envoy OAuth2 HTTP filter padding oracle vulnerability

Source: https://junglewise.ai/threats/cve-2026-47775-envoy-oauth2-http-filter-padding-oracle-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-26. Updated: 2026-06-26  
License: CC BY 4.0 with a link back

CVE-2026-47775 · Severity: medium · CVSS 6.8 · Published 2026-06-26

Envoy is a high-performance service proxy used to manage and secure network traffic for cloud applications. A security flaw in its OAuth2 authentication component allows an attacker to bypass security protections by exploiting how the system handles encrypted login data. If successful, an attacker could intercept a user's session and gain unauthorized access to their account and sensitive data.

Technologies: [Envoy Proxy Envoy](https://junglewise.ai/threats/technologies/envoy). Vendors: [Envoy Proxy](https://junglewise.ai/threats/vendors/envoy-proxy).

## Quick answers

**Is CVE-2026-47775 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-47775 being exploited in the wild.

**How severe is CVE-2026-47775?** Medium severity, with a CVSS score of 6.8, published 26 June 2026.

**Which products and versions are affected?** Envoy Proxy Envoy < 1.35.11, 1.36.0 to < 1.36.7, 1.37.0 to < 1.37.3, 1.38.0 to < 1.38.1.

**Is there a fix for CVE-2026-47775?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-47775 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-47775?** Check whether you run Envoy Proxy Envoy at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The OAuth2 HTTP filter in Envoy uses AES-256-CBC for cookie encryption without an authentication tag (HMAC or AEAD). The `/callback` endpoint returns distinct HTTP status codes (302 for success vs. 401 for padding failure), creating a padding oracle. An attacker who intercepts a victim's 'CodeVerifier' cookie and authorization code can perform a padding oracle attack in approximately 6,200 requests to recover the plaintext PKCE code_verifier. This allows the attacker to exchange the stolen code for a valid access token. The fix involves migrating to AES-256-GCM and ensuring uniform error responses.

## Affected products

- Envoy Proxy Envoy < 1.35.11, 1.36.0 to < 1.36.7, 1.37.0 to < 1.37.3, 1.38.0 to < 1.38.1

## Timeline

- 2026-03-13: disclosed: Vulnerability discovered and verified with E2E exploit
- 2026-03-15: other: Reported to Envoy GitHub Security Advisory
- 2026-06-26: advisory: CVE-2026-47775 published

## References

- [https://github.com/envoyproxy/envoy/security/advisories/GHSA-396h-jpq4-vc7p](https://github.com/envoyproxy/envoy/security/advisories/GHSA-396h-jpq4-vc7p)

## Related threats

- [Envoy HTTP upgrade connection poisoning](https://junglewise.ai/threats/cve-2026-73548-envoy-is-an-open-source-edge-and-service-proxy-designed-for-cloud)
- [Envoy use-after-free in HTTP OAuth2 filter](https://junglewise.ai/threats/cve-2026-48090-envoy-use-after-free-in-http-oauth2-filter)
- [Envoy denial of service via NULL pointer dereference in log formatting](https://junglewise.ai/threats/cve-2026-47220-envoy-denial-of-service-via-null-pointer-dereference-in-log)
- [Envoy Use-After-Free in ext_authz filter during stream teardown](https://junglewise.ai/threats/cve-2026-47205-envoy-use-after-free-in-ext-authz-filter-during-stream-teardown)
- [Envoy HTTP/3 to HTTP/1 request smuggling in downstream translation](https://junglewise.ai/threats/cve-2026-48743-envoy-http-3-to-http-1-request-smuggling-in-downstream)