Fix a couple of issues in DTLS ClientHello parsing.

[kareem-wolfssl]

Thanks to the Fuzz0x team for the report.

Description

Fixes zd#22219

Testing

Provided reproducers + built in tests

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[Copilot]

Pull request overview

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Tightens DTLS/TLS 1.3 ClientHello parsing to prevent out-of-bounds reads when consuming length-prefixed legacy fields (session_id and legacy_cookie), aligning error handling with fuzz-discovered edge cases.

Changes:

• Added explicit bounds checks before reading opaque-8 length fields in DoTls13SupportedVersions.
• Added bounds check and refactored cookieLen handling in DTLS DoTls13ClientHello parsing.

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[github-actions]

MemBrowse Memory Report

gcc-arm-cortex-m4-tls13

• FLASH: .text +64 B (+0.0%, 236,679 B / 262,144 B, total: 90% used)

gcc-arm-cortex-m7-pq

• FLASH: .text +64 B (+0.0%, 280,576 B / 1,048,576 B, total: 27% used)
  No memory changes detected for:
• gcc-arm-cortex-m0plus
• gcc-arm-cortex-m3
• gcc-arm-cortex-m4
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-crypto-only
• gcc-arm-cortex-m4-dtls13
• gcc-arm-cortex-m4-min-ecc
• gcc-arm-cortex-m4-openssl-compat
• gcc-arm-cortex-m4-pkcs7
• gcc-arm-cortex-m4-pq
• gcc-arm-cortex-m4-rsa-only
• gcc-arm-cortex-m4-sp-math
• gcc-arm-cortex-m4-tls12
• gcc-arm-cortex-m7
• gcc-arm-cortex-m7-tls13
• linuxkm-pie
• linuxkm-standard
• stm32-sim-stm32h753

[Fuzz0X]

I tested PR #11007 locally with my ASAN repro. Before the patch it hit the heap-buffer-overflow in
DoTls13SupportedVersions, and after applying the PR it just returns malformed buffer input error (-328) with no ASAN
crash.

[kareem-wolfssl]

Retest this please

[Fuzz0X]

I ran the original UDP repro a few times, and the heap-buffer-overflow no longer reproduces. The server now rejects it with -328 (malformed buffer input error) and exits without an ASAN abort.

I also ran make check and got no failures.

So the original OOB read still looks fixed to me.