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CVE-2021-34558 is an improper input-validation vulnerability in Go's standard-library crypto/tls package through Go 1.16.5. During an RSA-based TLS key exchange, crypto/tls does not properly verify that the public-key type in the server X.509 certificate matches the expected type. A malicious TLS server, or an attacker able to interfere with TLS traffic, can present a certificate of an incorrect type and cause the Go TLS client to panic.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository is a Proof-of-Concept (PoC) exploit for CVE-2021-34558, a vulnerability in Go's crypto/tls library (prior to version 1.16.6). The exploit consists of a Go program (main.go) that can run in two modes: as a malicious TLS server or as a client. The server is configured to present an ECDSA certificate while negotiating an RSA cipher suite, which is not a valid combination. When a vulnerable Go client connects to this server and attempts a TLS handshake, the client panics due to a type confusion bug (expecting an *rsa.PublicKey but receiving an *ecdsa.PublicKey). This results in a denial of service (DoS) for the client application. The repository includes a minor patch to the vendored utls library to enable the malicious handshake. The exploit is a pure PoC and does not provide remote code execution or privilege escalation, but demonstrates the crash and can be used to test for vulnerable Go deployments. The main entry point is main.go, and the exploit is executed by running the server and then the client as described in the README. No hardcoded external endpoints are present; the default is localhost, but this can be changed via command-line arguments.
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35 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A vulnerability addressed by the CIQ LTS 8.6 fuse-overlayfs security-update advisory.
A Go crypto/tls flaw in which a certificate of an unexpected type can panic a TLS client.
A Go crypto/tls denial-of-service vulnerability in which a certificate of an incorrect type causes a TLS client panic.
A Go crypto/tls flaw in which a certificate of the wrong type can cause a TLS client panic.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.