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CVE-2026-34181 is an authentication bypass vulnerability in the `go-pkcs12` library (software.sslmate.com/src/go-pkcs12), which affects versions 0.6.0 through 0.7.1. The issue stems from a failure to reject excessively-short PBMAC1 keys during PKCS12 file decoding. The vulnerable code resides in the `doPBMAC1` function within mac.go, which prior to patching did not validate the length of the PBMAC1 key. The four publicly exposed decoding functions—Decode, DecodeChain, DecodeTrustStore, and ToPEM—all internally call `doPBMAC1` for MAC verification, making them entry points for exploitation.
The vulnerability allows an attacker to craft a PKCS12 file with a PBMAC1 configuration specifying an HMAC key as short as a single byte. This collapses the key space to only 256 possibilities, enabling the attacker to forge a file that will be accepted by the vulnerable decoder with a 1-in-256 probability. The decoder incorrectly accepts the file even when the wrong password is provided, effectively bypassing password-based authentication. This issue was also reported in OpenSSL by Pavol Žáčik (Red Hat) and Alex Gaynor (Anthropic), and assigned the same CVE identifier. The patch, introduced in commit 03c441f6b0267f695ca02464133c0b373bf4dd55, adds a check ensuring the PBMAC1 key length is at least 20 octets, as recommended by RFC 9579. Users who only decode PKCS12 files from trusted sources are not affected.
DailyCVE Form:
Platform: go-pkcs12 library
Version: 0.6.0 – 0.7.1
Vulnerability: Authentication Bypass
Severity: Moderate (CVSS 6.3)
date: 2026-08-17
Prediction: Patch released 2026-08-17
What Undercode Say:
Check currently installed version go list -m software.sslmate.com/src/go-pkcs12 Update to patched version go get -u software.sslmate.com/src/[email protected] Clean up dependencies go mod tidy Verify vulnerability is resolved govulncheck ./...
Exploit: (Educational Purposes!)
// This is a simplified demonstration of the vulnerability concept.
// DO NOT use this for malicious purposes.
package main
import (
"software.sslmate.com/src/go-pkcs12"
)
// An attacker could craft a PKCS12 file where the PBMAC1
// parameters specify an excessively short KeyLength (e.g., 1).
// The vulnerable doPBMAC1 function would accept this file
// even with an incorrect password, as it did not validate
// the key length before the patch.
func exploitVulnerableDecode(data []byte, password string) {
// Prior to v0.7.2, this would accept a forged file
// with a 1-byte PBMAC1 key and wrong password.
_, _, err := pkcs12.Decode(data, password)
if err == nil {
// Authentication bypassed - attacker's certificate accepted
println("Authentication bypassed!")
}
}
Protection:
- Upgrade the `go-pkcs12` dependency to version v0.7.2 or higher immediately.
- If upgrading is not immediately possible, implement boundary checks to inspect the ASN.1 structure of PKCS12 containers before processing them.
- Enforce API rate-limiting on endpoints that ingest and parse PKCS12 files to mitigate multi-attempt brute-force attacks.
- Only decode PKCS12 files from trusted sources.
Impact:
An attacker can impersonate a legitimate user by providing a forged PKCS12 file containing attacker-controlled certificates and private keys. Services that rely on PKCS12 files for authentication—such as web servers, application servers, and certificate management systems—are at risk of accepting malicious credentials. The attack has a 1-in-256 success probability, meaning an attacker can succeed with limited computational resources through repeated attempts. The vulnerability does not affect FIPS modules, as the vulnerable code exists outside of certified cryptographic components.
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Sources:
Reported By: github.com
Extra Source Hub:
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