## If your build just died on SSL — start here If you landed here in a hurry, run these three commands first. This sequence *is* the diagnosis. ```bash # 1) Check the issuer and subject of the server (leaf) certificate (openssl x509 reads only the first certificate) openssl s_client -connect api.example.com:443 -showcerts /dev/null | openssl x509 -noout -issuer -subject # 2) 지금 쓰는 JVM이 신뢰하는 인증서 목록 조회 (JDK 9+) keytool -list -cacerts -storepass changeit | head -n 20 # 3) 그래도 모르겠으면 핸드셰이크 로그로 어디서 끊기는지 확인 java -Djavax.net.debug=ssl:handshake:verbose -jar app.jar ``` If command 1's `issuer=` is a **public CA (e.g. DigiCert, Let's Encrypt)** and it still fails, it's a JVM truststore / JDK version problem. If it's a **company or proxy name (Zscaler, BlueCoat, Fortinet, etc.)**, you're missing the corporate MITM proxy certificate. If `issuer` and `subject` are **the same**, it's a self-signed certificate. Every later branch starts from here. This post is a runbook specialized for the JVM, keytool, and truststores; the diagnostic tools differ from Go/Docker's `x509: certificate signed by unknown authority`. ## What this error actually is — two names, one problem `PKIX path building failed` and `SunCertPathBuilderException` are two names for the same incident. PKIX (Public-Key Infrastructure X.509) is the spec for validating certificate chains, and it means Java's default implementation could not build a **path from the server certificate up to a trusted root CA**. If "the code hasn't changed but it worked yesterday and fails today," it's almost never the code — **the environment changed**. The most common triggers in production: - You started hitting an **SSL inspection proxy** after moving offices or switching to remote work - The company rolled out a **MITM proxy such as Zscaler** as a security hardening measure - After a **JDK 8 → 17/21 LTS upgrade**, the cacerts path or contents changed - You moved to container builds and **did not inject the corporate CA into the truststore** ## Reading the stack trace line by line A typical stack trace wraps the exception in three layers. The deeper you go, the closer you get to the real cause. ```text javax.net.ssl.SSLHandshakeException: PKIX path building failed: # ← (1) TLS 핸드셰이크 단계에서 터짐 sun.security.validator.ValidatorException: # ← (2) 인증서 검증기가 거부 PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: # ← (3) 진짜 원인: 체인을 못 만듦 unable to find valid certification path to requested target ``` - **(1) SSLHandshakeException**: Failed during TLS negotiation. That's a signal the network connection itself succeeded (if the connection itself failed you'd see `ConnectException`). - **(2) ValidatorException**: The certificate the server presented was rejected during validation. You did reach the validation logic. - **(3) SunCertPathBuilderException**: The core. "unable to find valid certification path to requested target" = **the JVM does not trust the CA that issued the server certificate**. In other words, it doesn't mean "the certificate is forged"; it means "**the issuer is not in the trust list**." So the fix boils down to putting the right CA into the truststore. ## Cause-branching decision table Follow the table below based on the `issuer` value from the 30-second diagnosis. | Symptom / diagnostic clue | Likely cause | Next command | |---|---|---| | Issuer is a public CA but it still fails | JVM truststore corrupted/outdated, or a cacerts problem inside the JDK | Confirm the root exists with `keytool -list -cacerts`; apply the latest JDK patch | | Issuer is a company/proxy name (Zscaler, etc.) | Missing corporate SSL inspection (MITM) certificate | Import the proxy root CA with `-importcert` | | Issuer == Subject | Self-signed certificate | Import that server certificate directly into the truststore | | Root is present but it still fails | Intermediate CA missing (incomplete chain) | Inspect the chain with `-showcerts` and import the intermediate CA as well | | Fails only on a specific JDK | cacerts path/contents differ by JDK version; an old, unpatched JDK lacks a newer root CA | Check the version comparison table below; update to the latest JDK patch | | The message says `PKIX path validation failed ... validity check failed` | The certificate has expired (not a path-building problem) | Check the dates with `openssl x509 -in chain-1.pem -noout -dates`, then renew the server certificate | Run the three diagnostic commands in order and you'll know which row of the table you're on. ```bash # ① 서버가 실제로 내려주는 체인 전체 (중간 CA 포함 여부까지 보임) openssl s_client -connect api.example.com:443 -showcerts /dev/null # ② JVM이 신뢰하는 CA 목록에서 특정 발급자 검색 keytool -list -cacerts -storepass changeit | grep -i digicert # ③ 핸드셰이크에서 어느 인증서에서 끊기는지 상세 로그 java -Djavax.net.debug=ssl:handshake:verbose -jar app.jar ``` **Expected healthy result**: If ① shows `Verify return code: 0 (ok)`, trust is established at the OS level (the problem is JVM-only). If ② returns a grep hit, that CA is already registered. If ① is ok but Java still fails, that's the classic case of **the OS trust store and JVM cacerts being separate**. ## Recovery procedure — keytool import in practice ### Step 1: Extract the certificate you need Pull the root (or intermediate) CA presented by the proxy/server into PEM form. ```bash # Get the full chain the server sends with -showcerts and split it into one file per certificate (chain-1.pem, chain-2.pem ...) openssl s_client -connect api.example.com:443 -servername api.example.com -showcerts /dev/null \ | awk '/BEGIN CERTIFICATE/{n++; f="chain-" n ".pem"} f{print > f} /END CERTIFICATE/{close(f); f=""}' # Check subject and issuer of each file: chain-1 is the server (leaf), the rest are intermediate (or proxy) CAs for f in chain-*.pem; do echo "== $f"; openssl x509 -in "$f" -noout -subject -issuer; done # Pick the CA certificate to import and rename it (e.g. if the proxy CA is chain-2) cp chain-2.pem corp-root.pem # For a corporate proxy CA, the .cer/.pem distributed by the security team is usually the right file ``` Piping straight into `openssl s_client ... | openssl x509 -outform PEM` saves **only the first certificate (the server leaf)**, not the last one in the chain. Servers usually don't send the root CA either, so if you need the root, the file distributed by your security team or the CA is the accurate source. ### Step 2: Import into the truststore Two options: import into the JVM-wide cacerts (global), or create an app-specific custom truststore (isolated). ```bash # 방법 A) JVM 공용 cacerts에 등록 (JDK 9+에서 -cacerts 플래그 사용) keytool -importcert -alias corp-proxy -file corp-root.pem \ -cacerts -storepass changeit -noprompt # 방법 B) 앱 전용 커스텀 truststore 생성 (건드리기 부담스러울 때 권장) keytool -importcert -alias corp-proxy -file corp-root.pem \ -keystore app-truststore.jks -storepass mypass -noprompt # 실행 시 커스텀 truststore 지정 java -Djavax.net.ssl.trustStore=/opt/app/app-truststore.jks \ -Djavax.net.ssl.trustStorePassword=mypass -jar app.jar ``` **Expected healthy result**: You see `Certificate was added to keystore`, and the handshake succeeds when you restart the app. When you point `-Djavax.net.ssl.trustStore` at a custom truststore, the JVM trusts **only that file** instead of the default cacerts. If the file contains only your corporate CA, public sites break instead, so the safer approach is to copy the default cacerts into a PKCS12 file and add the corporate CA to it. ```bash # Copy the default cacerts into a PKCS12 file, then add the corporate CA (JDK 9+ path) keytool -importkeystore -srckeystore "$JAVA_HOME/lib/security/cacerts" -srcstorepass changeit \ -destkeystore app-truststore.p12 -deststoretype PKCS12 -deststorepass mypass keytool -importcert -alias corp-proxy -file corp-root.pem \ -keystore app-truststore.p12 -storetype PKCS12 -storepass mypass -noprompt java -Djavax.net.ssl.trustStore=/opt/app/app-truststore.p12 \ -Djavax.net.ssl.trustStorePassword=mypass \ -Djavax.net.ssl.trustStoreType=PKCS12 -jar app.jar ``` ### cacerts path and password by JDK version This is where people get lost most often during LTS migrations. JDK 8 has no `-cacerts` flag, so you must pass the path with `-keystore`. | JDK | cacerts path | Default password | keytool usage | |---|---|---|---| | 8 | `$JAVA_HOME/jre/lib/security/cacerts` | `changeit` | `-keystore $JAVA_HOME/jre/lib/security/cacerts` | | 11 | `$JAVA_HOME/lib/security/cacerts` | `changeit` | `-cacerts` is available | | 17 | `$JAVA_HOME/lib/security/cacerts` | `changeit` | `-cacerts` is available | | 21 | `$JAVA_HOME/lib/security/cacerts` | `changeit` | `-cacerts` is available | Starting with JDK 9 the JRE is gone, so the `jre/` subdirectory no longer exists. If you paste a JDK 8 script onto 11+ it will fail with "file not found" — watch out for that. ## Applying this to your build tool (Maven / Gradle) When the build itself dies, you must point the **JVM that runs the build tool** at the truststore. The app runtime JVM and the build JVM are separate. ```bash # Maven — 환경변수로 전달 export MAVEN_OPTS="-Djavax.net.ssl.trustStore=/opt/app/app-truststore.jks \ -Djavax.net.ssl.trustStorePassword=mypass" mvn clean package ``` ```properties # Gradle — gradle.properties 또는 명령행 org.gradle.jvmargs=-Djavax.net.ssl.trustStore=/opt/app/app-truststore.jks -Djavax.net.ssl.trustStorePassword=mypass ``` If dependencies can only be downloaded through a corporate proxy, also configure the proxy for Maven in `~/.m2/settings.xml`. ```xml corptrue https proxy.corp.com8080 ``` For Gradle, after setting the truststore, run `gradle build --refresh-dependencies` to ignore cached failures and download again. ## If it still fails after import — a mini re-branch FAQ **Q. I imported the root CA and it still fails the same way.** Most likely an incomplete chain. If the server **does not send the intermediate CA**, importing only the root will not complete the path, and the intermediate won't appear in the `-showcerts` output either. The real fix is to make the server send the full chain (fullchain). If you must work around it on the client, download the intermediate CA from the `CA Issuers` URL in the leaf certificate's AIA extension (`openssl x509 -in chain-1.pem -noout -ext authorityInfoAccess`) and import it under its own alias. **Q. Import fails with `alias already exists`.** The alias is already taken. Delete the existing one and import again. ```bash keytool -delete -alias corp-proxy -cacerts -storepass changeit keytool -importcert -alias corp-proxy -file corp-root.pem -cacerts -storepass changeit -noprompt ``` **Q. Import succeeded but the app still uses the old truststore.** The app is pointing at a different truststore. Check whether `-Djavax.net.ssl.trustStore` is set, and whether **the build JVM ≠ the runtime JVM**. If you're in a container, also check whether it was injected into the JDK cacerts inside the image. Confirm which truststore the running JVM is using with: ```bash java -Djavax.net.debug=ssl:trustmanager -jar app.jar 2>&1 | grep -i "trust store" ``` ## Preventing recurrence — and what you must never do The recurring root cause in container/CI environments is "the image has no corporate CA." Standardize the following. - Manage the corporate CA bundle (`corp-ca.pem`) as an artifact, and **bake it into cacerts at base-image build time** - Add a `keytool -importcert` step to the CI pipeline so the truststore is refreshed automatically - Expiry monitoring: renew the root/intermediate CA before it expires ```dockerfile # 베이스 이미지에서 사내 CA를 미리 주입하는 예시 COPY corp-ca.pem /tmp/corp-ca.pem RUN keytool -importcert -alias corp-ca -file /tmp/corp-ca.pem \ -cacerts -storepass changeit -noprompt ``` ⚠️ **Never do this**: In a hurry, overriding `TrustManager` with an all-trust implementation that accepts every certificate, turning off hostname verification, or otherwise disabling certificate validation leaves the app wide open to MITM attacks. Note that `-Dcom.sun.net.ssl.checkRevocation=false` only turns off revocation checking; it doesn't bypass chain validation and doesn't fix a PKIX error either. Even if you use it for temporary debugging, **never ship it to production**. The problem is not solved by turning validation off — only by putting the correct CA into the trust list. ### Closing checklist - [ ] Confirm the Issuer with `openssl s_client` → classify as public CA / proxy / self-signed - [ ] Confirm the cacerts path for your JDK version (8 is `jre/lib`, 11+ is `lib`) - [ ] Import the **intermediate CA as well as the root** so the chain is complete - [ ] Apply the truststore in all three places: build JVM, runtime JVM, and container image - [ ] Final check that no validation-bypass code remains ## Frequently asked questions (FAQ) **Q. Does `unable to find valid certification path to requested target` mean the certificate is forged?** No. In most cases it means the CA that issued the server certificate is not in the JVM's trust list (cacerts). Import that CA into the truststore and it will be resolved. **Q. The OS (and browser) can connect — why does only Java fail?** Because Java does not use the OS trust store; it uses **the JVM's own cacerts**. This is the classic situation where the corporate proxy CA was deployed to the OS but never made it into JVM cacerts, so you must register it separately with `keytool -importcert`. **Q. The keytool `-cacerts` option doesn't work.** The `-cacerts` flag is supported from JDK 9 onward. On JDK 8 you must specify the path directly: `-keystore $JAVA_HOME/jre/lib/security/cacerts -storepass changeit`.

#keytool

PKIX path building failed / SunCertPathBuilderException: A 30-Minute Fix Runbook