How severe is CVE-2019-9900?

CVE-2019-9900 has a CVSS 3.x base score of 8.3, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability low.

Is CVE-2019-9900 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2019-9900?

CVE-2019-9900 primarily affects Envoyproxy Envoy. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2019-9900?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2019-9900 published?

CVE-2019-9900 was published on 2019-04-25 and last updated on 2026-06-17.

CVE-2019-9900

CVE-2019-9900 is a high-severity vulnerability in Envoyproxy Envoy with a CVSS 3.x base score of 8.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-74.

Key facts

Severity: High (CVSS 3.x base score 8.3)
CVSS v2: 7.5
EPSS exploit prediction: 4% (90th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-74
Affected product: Envoyproxy Envoy
Published: 2019-04-25
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2019-9900?: 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.
How severe is CVE-2019-9900?: CVE-2019-9900 has a CVSS 3.x base score of 8.3, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability low.
Is CVE-2019-9900 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2019-9900?: CVE-2019-9900 primarily affects Envoyproxy Envoy. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2019-9900?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2019-9900 published?: CVE-2019-9900 was published on 2019-04-25 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*
cpe:2.3:a:redhat:openshift_service_mesh:-:*:*:*:*:*:*:*

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