This repository was archived by the owner on Oct 24, 2025. It is now read-only.
This repository was archived by the owner on Oct 24, 2025. It is now read-only.
AddressSanitizer: heap-buffer-overflow (OOB read) in Sass::Prelexer::skip_over_scopes (libsass/src/prelexer.hpp:69:14) #2661
Description
Hey there, I have discovered a single byte out-of-bands read (OOB) in libsass at: prelexer.hpp:69:14
Found when fuzzing commit 60f8391 of libsass, using commit aa6d5c6 of sassc as a harness.
Compile flags to reproduce:
CC=clang CXX=clang++ CFLAGS='-fsanitize=address -g -O2 -fno-omit-frame-pointer' CXXFLAGS=$CFLAGS make -C sassc -j8 System information:
$ uname -a Linux s127422 3.13.0-137-generic #186-Ubuntu SMP Mon Dec 4 19:09:19 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux This bug was found to be in libsass releases from 3.2.0 until the commit listed above.
You can find a collection of PoC files that trigger the bug here.
The full ASAN report is shown below:
↳ sassc/bin/sassc < crash.file ================================================================= ==12294==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60700000dffc at pc 0x000000804138 bp 0x7ffd55ba7d20 sp 0x7ffd55ba7d18 READ of size 1 at 0x60700000dffc thread T0 #0 0x804137 in char const* Sass::Prelexer::skip_over_scopes<&(char const* Sass::Prelexer::exactly<&Sass::Constants::hash_lbrace>(char const*)), &(char const* Sass::Prelexer::exactly<&Sass::Constants::rbrace>(char const*))>(char const*, char const*) /home/glenn/temp/findsass/libsass/prelexer.hpp:68:14 #1 0x78ca33 in char const* Sass::Parser::peek<&Sass::Prelexer::interpolant>(char const*) /home/glenn/temp/findsass/libsass/parser.hpp:114:14 #2 0x78ca33 in Sass::Parser::lookahead_for_selector(char const*) /home/glenn/temp/findsass/libsass/parser.cpp:2025 #3 0x76c877 in Sass::Parser::parse() /home/glenn/temp/findsass/libsass/parser.cpp:152:36 #4 0x5271a0 in Sass::Context::parse_file() /home/glenn/temp/findsass/libsass/context.cpp:323:20 #5 0x52b276 in Sass::Context::parse_string() /home/glenn/temp/findsass/libsass/context.cpp:363:14 #6 0x4fbfad in sass_parse_block(Sass_Compiler*) /home/glenn/temp/findsass/libsass/sass_context.cpp:505:16 #7 0x4fbfad in sass_compiler_parse /home/glenn/temp/findsass/libsass/sass_context.cpp:652 #8 0x4fae24 in sass_compile_context(Sass_Context*, Sass::Context::Data) /home/glenn/temp/findsass/libsass/sass_context.cpp:536:7 #9 0x4faa3c in sass_compile_data_context /home/glenn/temp/findsass/libsass/sass_context.cpp:623:12 #10 0x4effcf in compile_stdin /home/glenn/temp/findsass/sassc/sassc.c:86:5 #11 0x4f132f in main /home/glenn/temp/findsass/sassc/sassc.c:282:18 #12 0x7f5eddf8e82f in __libc_start_main /build/glibc-Cl5G7W/glibc-2.23/csu/../csu/libc-start.c:291 #13 0x41e4a8 in _start (/home/glenn/temp/findsass/sassc/bin/sassc+0x41e4a8) 0x60700000dffc is located 0 bytes to the right of 76-byte region [0x60700000dfb0,0x60700000dffc) allocated by thread T0 here: #0 0x4be958 in realloc (/home/glenn/temp/findsass/sassc/bin/sassc+0x4be958) #1 0x4efed2 in compile_stdin /home/glenn/temp/findsass/sassc/sassc.c:68:25 #2 0x4f132f in main /home/glenn/temp/findsass/sassc/sassc.c:282:18 #3 0x7f5eddf8e82f in __libc_start_main /build/glibc-Cl5G7W/glibc-2.23/csu/../csu/libc-start.c:291 SUMMARY: AddressSanitizer: heap-buffer-overflow /home/glenn/temp/findsass/libsass/prelexer.hpp:68:14 in char const* Sass::Prelexer::skip_over_scopes<&(char const* Sass::Prelexer::exactly<&Sass::Constants::hash_lbrace>(char const*)), &(char const* Sass::Prelexer::exactly<&Sass::Constants::rbrace>(char const*))>(char const*, char const*) Shadow bytes around the buggy address: 0x0c0e7fff9ba0: fa fa 00 00 00 00 00 00 00 00 00 fa fa fa fa fa 0x0c0e7fff9bb0: 00 00 00 00 00 00 00 00 00 fa fa fa fa fa 00 00 0x0c0e7fff9bc0: 00 00 00 00 00 00 00 fa fa fa fa fa 00 00 00 00 0x0c0e7fff9bd0: 00 00 00 00 00 fa fa fa fa fa 00 00 00 00 00 00 0x0c0e7fff9be0: 00 00 00 fa fa fa fa fa 00 00 00 00 00 00 00 00 =>0x0c0e7fff9bf0: 00 fa fa fa fa fa 00 00 00 00 00 00 00 00 00[04] 0x0c0e7fff9c00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c0e7fff9c10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c0e7fff9c20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c0e7fff9c30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c0e7fff9c40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa Shadow byte legend (one shadow byte represents 8 application bytes): Addressable: 00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone: fa Heap right redzone: fb Freed heap region: fd Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 Stack partial redzone: f4 Stack after return: f5 Stack use after scope: f8 Global redzone: f9 Global init order: f6 Poisoned by user: f7 Container overflow: fc Array cookie: ac Intra object redzone: bb ASan internal: fe Left alloca redzone: ca Right alloca redzone: cb ==12294==ABORTING