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CVE-2019-9900

28
FAUCET Score

CVE-2019-9900 describes a vulnerability in Envoy 1.9.0 and earlier where embedded null characters in HTTP/1.x header values are not properly rejected, potentially allowing attackers to bypass header matching rules. This high-severity vulnerability (CVSS 8.3) affects envoyproxy envoy, envoyproxy openshift_service_mesh, redhat envoy, and redhat openshift_service_mesh, enabling unauthorized access to resources with low attack complexity and no user interaction. While there is no evidence of active exploitation, public exploit code, or inclusion in the KEV catalog, the vulnerability has garnered some community discussion, indicating awareness.

Impacted Technologies

VendorProductVersion(s)CPE
<= 1.9.0CPE matchmatch criteria
cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:a:redhat:openshift_service_mesh:-:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

6.5MEDIUM

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:L

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
LOW
Exploitability Score
2.2
Impact Score
3.7
CvssVersion
3.0

Exploit Intelligence

EPSS Score
3.73%
Probability of exploitation in next 30 days
EPSS Percentile
88.7%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0373 is in the 80th percentile among its peer group of 51,553 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

redhatpatch availablevia redhat_api
Product: OpenShift Service Mesh Tech PreviewFixed in: servicemesh-proxy-0:0.9.1-1.el7
View patch
github_advisoryworkaround availablevia nvd_reference
View patch

Vendor Advisories (1)

redhatCVE-2019-9900Important

istio/envoy: Authorization bypass via null characters injection in HTTP/1.x

Apr 5, 2019

References

access.redhat.com / errata/RHSA-2019:0741
Third Party Advisory
github.com / envoyproxy/envoy/issues/6434
ExploitIssue TrackingThird Party Advisory
github.com / envoyproxy/envoy/security/advisories/GHSA-x74r-f4mw-c32h
ExploitMitigationThird Party Advisory
groups.google.com / forum
envoyproxy.io / docs/envoy/v1.9.1/intro/version_history
Release NotesVendor Advisory