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Fencer Vulns
medium 6.5

CVE-2019-9900 json

When parsing HTTP/1.x header values, Envoy 1.9.0 and before does not reject embedded zero characters (NUL, ASCII 0x0).

published 2019-04-25 7 y ago modified 2026-06-17 4 mo ago also EUVD-2019-19256

cvss
6.5
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
3.7%
EPSS 3.7% chance of exploitation in 30 days, percentile 89%
public exploits
0
none known

Summary

When parsing HTTP/1.x header values, Envoy 1.9.0 and before does not reject embedded zero characters (NUL, ASCII 0x0). This allows remote attackers crafting header values containing embedded NUL characters to potentially bypass header matching rules, gaining access to unauthorized resources.

Patch / fix

  • servicemesh-proxy service mesh 0 0.9.1-1.el7

red hat advisories RHSA-2019:0741

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2019-9900 updated cvss 8.3

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

  • Red Hat OpenShift Service Mesh 0 Tech Preview servicemesh-proxy 0.9.1-1.el7
    fixed: vendor fix RHSA-2019:0741

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

3.73% chance of exploitation in the next 30 days, higher than 89% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/envoyproxy/envoy/issues/6434 referenced PoC, tagged "exploit" by a source, unverified
  • github.com https://github.com/envoyproxy/envoy/security/advisories/GHSA-x74r-f4mw-c32h referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.0 6.5 CVSS:3.0/AC:H/AV:N/A:L/C:L/I:L/PR:N/S:C/UI:N
NVD 3.1 8.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L
CNA 3.0 6.5 CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:L
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

Classification

Weakness
  • CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.