CVE-2021-43826 Crash when tunneling TCP over HTTP in Envoy

What is CVE-2021-43826?

CVE-2021-43826 is a high-severity use after free vulnerability in Envoyproxy Envoy, published on 22 Feb 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Envoy is an open source edge and service proxy, designed for cloud-native applications. In affected versions of Envoy a crash occurs when configured for :ref:`upstream tunneling <envoy_v3_api_field_extensions.filters.network.tcp_proxy.v3.TcpProxy.tunneling_config>` and the downstream connection disconnects while the the upstream connection or http/2 stream is still being established. There are no workarounds for this issue. Users are advised to upgrade.

Weakness: CWE-416

Which versions are affected by CVE-2021-43826?

1 open source package ship an affected version, including envoy. It affects 1 product.

Products include Envoyproxy Envoy.

How do I fix CVE-2021-43826?

Upgrade envoy to a fixed version for your release line: 1.18.6, 1.19.3, 1.20.2 or 1.21.1.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2021-43826 being exploited?

There is no known exploitation of CVE-2021-43826 in the wild and no public exploit code.

Other vulnerabilities in Envoyproxy Envoy

• CVE-2022-29226 Trivial authentication bypass in Envoy Critical 10.0
• CVE-2019-18801 Memory corruption in n/a Critical 9.8
• CVE-2019-18802 Security feature bypass in n/a Critical 9.8
• CVE-2020-35470 Information disclosure in n/a High 8.8
• CVE-2024-23324 Envoy ext auth can be bypassed when Proxy protocol filter sets invalid UTF-8 metadata High 8.6

All Envoyproxy Envoy vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-envoy-2021-43826, GHSA-cmx3-fvgf-83mf.