From 2290143edc27486196815874dca5a528c118a73f Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Fri, 19 Jun 2026 18:22:20 +0200 Subject: [PATCH 3/3] resolv: Fix buffer overreads in ns_sprintrrf (CVE-2026-6238) Check that the RDATA payload does not require more than RDATALEN bytes while processing it. The fixes cover A6, LOC records. (CERT, TKEY, TSIG were fixed before, by switching to the generic formatter.) The vulnerable LOC record handling was first introduced before glibc 2.0, in commit ee188d555b8c32ad9704a7440cab400af967292f. CERT, TSIG, TKEY handling came with commit b43b13ac2544b11f35be301d1589b51a8473e32b, released with glibc 2.2. A6 record handling was introduced in commit 91633816430e7ec5a19fe3ff510a7c4822a9557e ("* resolv/ns_print.c (ns_sprintrrf): Handle ns_t_a6 and ns_t_opt."), which went into glibc 2.7. This fixes bug 34069. Reviewed-by: Carlos O'Donell Reviewed-by: Adhemerval Zanella (cherry picked from commit a7b60d23bbb56eaef59f4962e4140062e552600a) --- resolv/ns_print.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/resolv/ns_print.c b/resolv/ns_print.c index 8c876b147e..6832255a25 100644 --- a/resolv/ns_print.c +++ b/resolv/ns_print.c @@ -318,7 +318,8 @@ ns_sprintrrf(const u_char *msg, size_t msglen, case ns_t_loc: { char t[255]; - /* XXX protocol format checking? */ + if (rdlen != 16) + goto formerr; (void) loc_ntoa(rdata, t); T(addstr(t, strlen(t), &buf, &buflen)); break; @@ -452,13 +453,14 @@ ns_sprintrrf(const u_char *msg, size_t msglen, /* address suffix: provided only when prefix len != 128 */ if (pbit < 128) { - if (rdata + pbyte >= edata) goto formerr; + unsigned int bytelen = sizeof(a) - pbyte; + if (edata - rdata < bytelen) goto formerr; memset(&a, 0, sizeof(a)); - memcpy(&a.s6_addr[pbyte], rdata, sizeof(a) - pbyte); + memcpy(&a.s6_addr[pbyte], rdata, bytelen); if (inet_ntop (AF_INET6, &a, buf, buflen) == NULL) return -1; addlen(strlen(buf), &buf, &buflen); - rdata += sizeof(a) - pbyte; + rdata += bytelen; } /* prefix name: provided only when prefix len > 0 */ -- 2.54.0