BUG/CRITICAL: mux-h2: re-check the frame length when PRIORITY is used
Tim Düsterhus reported a possible crash in the H2 HEADERS frame decoder
when the PRIORITY flag is present. A check is missing to ensure the 5
extra bytes needed with this flag are actually part of the frame. As per
RFC7540#4.2, let's return a connection error with code FRAME_SIZE_ERROR.
Many thanks to Tim for responsibly reporting this issue with a working
config and reproducer. This issue was assigned CVE-2018-20615.
This fix must be backported to 1.9 and 1.8.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index dc67bc6..20ff988 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -3316,6 +3316,11 @@
goto fail;
}
+ if (flen < 5) {
+ h2c_error(h2c, H2_ERR_FRAME_SIZE_ERROR);
+ goto fail;
+ }
+
hdrs += 5; // stream dep = 4, weight = 1
flen -= 5;
}