mbedtls: update to 3.6.7

mbedtls: update to 3.6.7

This version fixes security issues and bugs.

Security fixes:
* Fix a side channel in RSA PKCS#1 v1.5 decryption. (CVE-2026-50587)
* Fix a bug where transcript-hash computation errors during TLS 1.2 extended master secret calculation could be ignored instead of causing the handshake to fail. (CVE-2026-50581)
* Fix a TLS 1.3 server-side error-handling bug affecting session ticket generation. (CVE-2026-50640)
* Fix renegotiation failing and potentially causing a buffer overflow in DTLS when badmac_limit is enabled. (CVE-2026-50713)
* Reject ChaCha20 operations that would make the 32-bit block counter wrap around, which could otherwise reuse keystream and compromise confidentiality. (CVE-2026-50584)
* Fixed a TLS 1.3 record-boundary validation issue that could allow unauthenticated plaintext data to be processed across a key change.
* Fix a possible buffer overflow in mbedtls_ecdh_calc_secret() (CVE-2026-35336)
* Fix a remote buffer overflow in (D)TLS with ECDHE-PSK cipher suites when CBC is disabled. (CVE-ID-50580)
* Fix a side channel in ECC computations that allows a powerful local attacker (typically, untrusted OS attacking a secure enclave) to fully recover long-term secret keys). (CVE-2026-54435)
* Fix a potential information disclosure in TLS 1.2 servers using session tickets. (CVE-2026-50586)
* Fix timing side channel in RSA key generation, prime generation and primality testing, on platforms where division is not constant-time.
* Fix a 1-byte buffer overread when parsing a malformed ECC public key in the PK module. (CVE-2026-50583)
* Fix an out-of-bounds read when parsing TLS 1.2 ECJPAKE ServerKeyExchange messages. (CVE-2026-50588)
* Fix a use-after-free/double-free risk in mbedtls_pkcs7_free() when reusing an mbedtls_pkcs7 context across parse -> free -> parse -> free cycles. (CVE-2026-50579)
* PKCS7 now rejects weak hash algorithms (RIPEMD160, MD5, SHA-1, SHA-224, SHA3-224) on signature verification.
* Improved documentation of mbedtls_ssl_conf_sig_algs() to emphasize that this function only sets signature algorithms that are enforced during TLS key exchange and not on certificate verification. (CVE-2026-54441)
* Ensure 'dtls_srtp_info' field from 'mbedtls_ssl_context' is properly zeroized when mbedtls_ssl_session_reset() is called. (CVE-2026-50585)
* Fix a bug where mbedtls_ssl_read() and mbedtls_ssl_write() could return 1 instead of an error code if the random generator failed when a server called these functions before the end of a TLS 1.3 handshake.
* Fix TLS 1.3 clients to reject a HelloRetryRequest whose selected group was not advertised in the original ClientHello. (CVE-2026-25832)
* Fix two bugs in the X.509 certificate parser that caused some inputs with a malformed basicConstraints extension to be accepted. (CVE-2026-49300)

Full release notes: https://github.com/Mbed-TLS/mbedtls/releases/tag/mbedtls-3.6.7

Remove backported upstream patches that are included in this release.

Signed-off-by: Magnus Kroken <mkroken@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24131
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>