telnet: use pointer[0] for "unknown" option instead of pointer[i] #18851
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i is taken from pointer[length-2] (often the IAC byte) before we do length -= 2, so using pointer[i] indexes an arbitrary/stale byte unrelated to the option code. pointer[0] is the suboption’s option code per the telnet SB format, so printing pointer[0] yields correct, stable diagnostics.
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Note: An initial analysis showed this may actually patch an OOB read, but I think that isn't possible. |
bagder
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Oct 5, 2025
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Thanks! |
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i is taken from pointer[length-2] (often the IAC byte) before we do length -= 2, so using pointer[i] indexes an arbitrary/stale byte unrelated to the option code. pointer[0] is the suboption’s option code per the telnet SB format, so printing pointer[0] yields correct, stable diagnostics.