Random832 &lt;random832(a)fastmail.com&gt; wrote: Even without that check V7 wouldn't be vulnerable. In V6, the vulnerability occurs in psig() when the signal action is reset: http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/sys/ken/sig.c rp = u.u_procp; n = rp->p_sig; rp->p_sig = 0; if((p=u.u_signal[n]) != 0) { u.u_error = 0; if(n != SIGINS && n != SIGTRC) u.u_signal[n] = 0; /* if n < 0 this can overwrite u.u_uid */ In V7, instead of a single pending signal, there is a bitmap of pending signals, so the corresponding code is, http://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/sys/sys/sig.c n = fsig(rp); if (n==0) return; rp->p_sig &= ~(1<<(n-1)); if((p=u.u_signal[n]) != 0) { u.u_error = 0; if(n != SIGINS && n != SIGTRC) u.u_signal[n] = 0; /* always within the array bounds */ Tony. -- f.anthony.n.finch &lt;dot(a)dotat.at&gt; http://dotat.at/ - I xn--zr8h punycode Viking, North Utsire, South Utsire, Northeast Forties: Variable becoming southeasterly 3 or 4, increasing 5 to 7, perhaps gale 8 later. Slight or moderate becoming moderate or rough later. Fog patches, rain later. Moderate, occasionally very poor.