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Vulnerability record · CVE-2024-27919 · published 4 April 2024

CVE-2024-27919: Envoy HTTP/2 CONTINUATION frame flood causes memory exhaustion DoS

Envoyproxy · Envoy

Envoy versions 1.29.0 and 1.29.1 fail to reset an HTTP/2 request when header map limits are exceeded, allowing an attacker to send CONTINUATION frames without END_HEADERS and consume unbounded memory. This is a regression introduced in 1.29.0 and fixed in 1.29.2. The result is denial of service through memory exhaustion on the proxy.

7.5 CVSS 3.1 High EPSS 87% · top 0.3% CWE-390 · CWE-390
7.5CVSS 3.1 base score
87%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
9References
17 Jun 2026Last modified by NVD

Description

Envoy is a cloud-native, open-source edge and service proxy. In versions 1.29.0 and 1.29.1, theEnvoy HTTP/2 protocol stack is vulnerable to the flood of CONTINUATION frames. Envoy's HTTP/2 codec does not reset a request when header map limits have been exceeded. This allows an attacker to send an sequence of CONTINUATION frames without the END_HEADERS bit set causing unlimited memory consumption. This can lead to denial of service through memory exhaustion. Users should upgrade to versions 1.29.2 to mitigate the effects of the CONTINUATION flood. Note that this vulnerability is a regression in Envoy version 1.29.0 and 1.29.1 only. As a workaround, downgrade to version 1.28.1 or earlier or disable HTTP/2 protocol for downstream connections.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 18 September 2026. Confidence: high.

high priorityCVSS 7.5 high severity, unauthenticated network-reachable availability impact, very high EPSS, and a narrow affected version range with a clear patch.

What it is

Envoy versions 1.29.0 and 1.29.1 fail to reset an HTTP/2 request when header map limits are exceeded, allowing an attacker to send CONTINUATION frames without END_HEADERS and consume unbounded memory. This is a regression introduced in 1.29.0 and fixed in 1.29.2. The result is denial of service through memory exhaustion on the proxy.

Impact

An unauthenticated remote attacker can exhaust Envoy memory, degrading or halting proxied services. No data confidentiality or integrity impact is described; the effect is availability loss.

Attack surface

Reachable over the network via the HTTP/2 protocol stack on downstream connections; no authentication or user interaction is required per the CVSS vector AV:N/PR:N/UI:N. The flaw is in the HTTP/2 codec's handling of header map limits.

Exploitation

Not listed in CISA KEV and no ransomware usage documented. EPSS is very high (0.86746, 99.7th percentile), and references include patch and advisory tags but no public exploit tag.

What to do

  • Upgrade Envoy to 1.29.2 or later.
  • If upgrade is not possible, downgrade to 1.28.1 or earlier.
  • As a workaround, disable HTTP/2 for downstream connections.
  • Apply the referenced patch commit if maintaining a custom build.
  • Monitor Envoy memory usage and restart or shed load if exhaustion is observed.

Detection

  • Alert on sustained growth in Envoy process memory or container memory near limits.
  • Inspect HTTP/2 traffic for long sequences of CONTINUATION frames without END_HEADERS.
  • Track HTTP/2 header map limit exceed events and request resets in Envoy logs.
  • Correlate spikes in downstream HTTP/2 connections with proxy latency and 5xx responses.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://www.openwall.com/lists/oss-security/2024/04/03/16 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2024/04/05/3 Mailing List
https://github.com/envoyproxy/envoy/commit/57a02565532c18eb9df972a3e8974be3ae59f2d5 Patch
https://github.com/envoyproxy/envoy/security/advisories/GHSA-gghf-vfxp-799r PatchThird Party Advisory
http://www.openwall.com/lists/oss-security/2024/04/03/16 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2024/04/05/3 Mailing List
https://github.com/envoyproxy/envoy/commit/57a02565532c18eb9df972a3e8974be3ae59f2d5 Patch
https://github.com/envoyproxy/envoy/security/advisories/GHSA-gghf-vfxp-799r PatchThird Party Advisory
https://www.kb.cert.org/vuls/id/421644

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2024-27919), CISA KEV, FIRST EPSS (scores of 2026-09-24). This page is refreshed as NVD updates the record.