CVE-2021-29258Network attack vector

Remote crash via empty HTTP/2 metadata

Published May 20, 2021 · Updated Aug 3, 2024

Reachable assertion in Envoy HTTP/2 Metadata 1.14.6, 1.15.3, 1.16.2, and 1.17.1 allows remote attackers to crash Envoy. The HTTP/2 metadata path processes an empty decoded map despite an invariant that metadata must contain an entry, triggering the reachable assertion. The HTTP/2 Metadata frame feature must be enabled; one crafted request terminates the Envoy process and interrupts proxied service.

CVSS severity7.5
High
EPSS probability1.77%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reachable assertion in Envoy HTTP/2 Metadata 1.14.6, 1.15.3, 1.16.2, and 1.17.1 allows remote attackers to crash Envoy. The HTTP/2 metadata path processes an empty decoded map despite an invariant that metadata must contain an entry, triggering the reachable assertion. The HTTP/2 Metadata frame feature must be enabled; one crafted request terminates the Envoy process and interrupts proxied service.

The record

CVE
CVE-2021-29258
Published
May 20, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-617, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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