From b80131fcf582ecc8e8c1b97e6051bb324bb8bef8 Mon Sep 17 00:00:00 2001 From: Stefan Metzmacher Date: Sun, 15 Mar 2026 19:15:14 +0100 Subject: [PATCH] CVE-2026-4480: s3:printing: mask and/or single quote jobname passed as %J to "print command" Fix an unauthenticated remote code execution vulnerability with printing set to anything *but* cups and iprint, for example "lprng", so that "print command" is executed upon job submission. If the client-controlled job name is handed to the "print command" via %J, rpcd_spoolssd passes this to the shell without escaping critical characters. Using single quotes (directly) around %J, '%J' would avoid the problem, we now try to autodetect if we can use '%J' implicitly or we fallback to a fixed "__CVE-2026-4480_FallbackJobname__" string instead of the client provided jobname. BUG: https://bugzilla.samba.org/show_bug.cgi?id=16033 Signed-off-by: Stefan Metzmacher Reviewed-by: Douglas Bagnall --- source3/printing/print_generic.c | 107 +++++++++++++++++++++++++++---- 1 file changed, 94 insertions(+), 13 deletions(-) diff --git a/source3/printing/print_generic.c b/source3/printing/print_generic.c index 855de4ca1f36..a14d1d441df3 100644 --- a/source3/printing/print_generic.c +++ b/source3/printing/print_generic.c @@ -19,6 +19,7 @@ #include "includes.h" #include "lib/util/util_file.h" +#include "lib/util/util_str_escape.h" #include "printing.h" #include "smbd/proto.h" #include "source3/lib/substitute.h" @@ -207,6 +208,52 @@ static int generic_queue_get(const char *printer_name, return qcount; } +static const char *replace_print_cmd_J(TALLOC_CTX *mem_ctx, + const char *orig_cmd, + const char *unsafe_jobname, + const char *fallback_jobname) +{ + char *cmd = NULL; + bool modified = false; + bool masked = false; + bool mixed_fallback = false; + + /* + * This replaces unsafe characters with '_'. + * We also mask forward and backslash here. + * + * Then it replaces %J with an single quoted + * version of the masked jobname or it falls + * back to fallback_jobname is the print command + * uses strange mixed quoting. + */ + +#define JOBNAME_UNSAFE_CHARACTERS \ + STRING_SUB_UNSAFE_CHARACTERS "/\\" + + cmd = talloc_string_sub_unsafe(mem_ctx, + orig_cmd, + 'J', + unsafe_jobname, + JOBNAME_UNSAFE_CHARACTERS, + '_', + fallback_jobname, + &modified, + &masked, + &mixed_fallback); + if (cmd == NULL) { + return NULL; + } + + /* + * The caller already checked talloc_string_sub_mixed_quoting() + * and warned the admin, so we don't check mixed_fallback + * here + */ + + return cmd; +} + /**************************************************************************** Submit a file for printing - called from print_job_end() ****************************************************************************/ @@ -222,11 +269,12 @@ static int generic_job_submit(int snum, struct printjob *pjob, char *print_directory = NULL; char *wd = NULL; char *p = NULL; - char *jobname = NULL; + const char *print_cmd = NULL; TALLOC_CTX *ctx = talloc_tos(); fstring job_page_count, job_size; print_queue_struct *q = NULL; print_status_struct status; + const char *jobname = "No Document Name"; /* we print from the directory path to give the best chance of parsing the lpq output */ @@ -255,24 +303,48 @@ static int generic_job_submit(int snum, struct printjob *pjob, return -1; } - jobname = talloc_strdup(ctx, pjob->jobname); - if (!jobname) { - ret = -1; - goto out; + if (pjob->jobname[0] != '\0') { + jobname = pjob->jobname; } - jobname = talloc_string_sub(ctx, jobname, "'", "_"); - if (!jobname) { - ret = -1; - goto out; + + print_cmd = lp_print_command(snum); + if (print_cmd != NULL) { + const char *invalid_jobname = "__CVE-2026-4480_FallbackJobname__"; + + if (talloc_string_sub_mixed_quoting(print_cmd, 'J')) { + /* + * The admin used a strange mixture of + * single and double quotes, fallback + * to InvalidDocumentName and warn about + * it, so that the admin can adjust to + * the use single quotes directly around %J, + * e.g. '%J'. + */ + jobname = invalid_jobname; + D_WARNING("CVE-2026-4480: printer %s " + "strange quoting in 'print command', " + "falling back to jobname=%s, " + "use testparm to fix the configuration\n", + lp_printername(talloc_tos(), lp_sub, snum), + invalid_jobname); + } + + print_cmd = replace_print_cmd_J(ctx, + print_cmd, + jobname, + invalid_jobname); + if (!print_cmd) { + ret = -1; + goto out; + } } fstr_sprintf(job_page_count, "%d", pjob->page_count); fstr_sprintf(job_size, "%zu", pjob->size); /* send it to the system spooler */ ret = print_run_command(snum, lp_printername(talloc_tos(), lp_sub, snum), True, - lp_print_command(snum), NULL, + print_cmd, NULL, "%s", p, - "%J", jobname, "%f", p, "%z", job_size, "%c", job_page_count, @@ -293,17 +365,26 @@ static int generic_job_submit(int snum, struct printjob *pjob, int i; for (i = 0; i < ret; i++) { if (strcmp(q[i].fs_file, p) == 0) { + char *le_jobname = + log_escape(talloc_tos(), jobname); + pjob->sysjob = q[i].sysjob; DEBUG(5, ("new job %u (%s) matches sysjob %d\n", - pjob->jobid, jobname, pjob->sysjob)); + pjob->jobid, le_jobname, pjob->sysjob)); + + TALLOC_FREE(le_jobname); break; } } ret = 0; } if (pjob->sysjob == -1) { + char *le_jobname = log_escape(talloc_tos(), jobname); + DEBUG(2, ("failed to get sysjob for job %u (%s), tracking as " - "Unix job\n", pjob->jobid, jobname)); + "Unix job\n", pjob->jobid, le_jobname)); + + TALLOC_FREE(le_jobname); }