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Rewrite: fix buffer overflow with overlapping captures

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When the rewrite replacement string had no variables, but had
overlapping captures, the length of the allocated buffer could be
smaller than the replacement string.  This could happen either
when the "redirect" parameter is specified, or when arguments are
present in the replacement string.

The following configurations resulted in heap buffer overflow when
using URI "/++++++++++++++++++++++++++++++":

    location / {
        rewrite ^/((.*))$ http://127.0.0.1:8080/$1$2 redirect;
        return 200 foo;
    }

    location / {
        rewrite ^/((.*))$ http://127.0.0.1:8080/?$1$2;
        return 200 foo;
    }

Reported by Mufeed VH of Winfunc Research.
This commit is contained in:
Roman Arutyunyan 2026-05-14 18:42:18 +04:00 • committed by Roman Arutyunyan
parent 475732a3f9
commit ca4f92a274
1 changed files with 13 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

20
src/http/ngx_http_script.c
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@ -1037,6 +1037,8 @@ ngx_http_script_start_args_code(ngx_http_script_engine_t *e)
void
ngx_http_script_regex_start_code(ngx_http_script_engine_t *e)
{
int *cap;
u_char *p;
size_t len;
ngx_int_t rc;
ngx_uint_t n;
@ -1143,15 +1145,19 @@ ngx_http_script_regex_start_code(ngx_http_script_engine_t *e)
if (code->lengths == NULL) {
e->buf.len = code->size;
if (code->uri) {
if (r->ncaptures && (r->quoted_uri || r->plus_in_uri)) {
e->buf.len += 2 * ngx_escape_uri(NULL, r->uri.data, r->uri.len,
NGX_ESCAPE_ARGS);
}
}
cap = r->captures;
p = r->captures_data;
for (n = 2; n < r->ncaptures; n += 2) {
e->buf.len += r->captures[n + 1] - r->captures[n];
e->buf.len += cap[n + 1] - cap[n];
if (code->uri) {
if (r->quoted_uri || r->plus_in_uri) {
e->buf.len += 2 * ngx_escape_uri(NULL, &p[cap[n]],
cap[n + 1] - cap[n],
NGX_ESCAPE_ARGS);
}
}
}
} else {