heap-buffer-overflow in wasm::WATParser::Lexer::peek() at parser/lexer.h:137 (main branch @3ef8d19)

Summary

ASan detects a heap-buffer-overflow (out-of-bounds read) in the WAT parser when parsing malformed input with wasm-ctor-eval.

Affected Version

• Branch: main
• Commit: 3ef8d19 (2026-04-21 latest)
• Tool: wasm-ctor-eval
• Build type: Debug + AddressSanitizer

Reproduction

mkdir build && cd build

cmake \
  -DCMAKE_C_COMPILER=/home/AFLplusplus/afl-clang-fast \
  -DCMAKE_CXX_COMPILER=/home/AFLplusplus/afl-clang-fast++ \
  -DCMAKE_C_FLAGS="-O0 -g -fno-omit-frame-pointer -fsanitize=address -Wno-error" \
  -DCMAKE_CXX_FLAGS="-std=c++20 -O0 -g -fno-omit-frame-pointer -fsanitize=address -Wno-bitwise-instead-of-logical -Wno-ambiguous-reversed-operator -Wno-error" \
  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address -no-pie -pthread -ldl -lm" \
  -DCMAKE_BUILD_TYPE=Debug \
  -DBUILD_TESTS=OFF \
  -DBUILD_TOOLS=ON \
  -DENABLE_BYESAN=OFF \
  ..

make -j$(nproc)

./wasm-ctor-eval poc

ASan Error Log

==3262527==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60b000001549 at pc 0x7ffff5e55cce bp 0x7fffffff7650 sp 0x7fffffff7648
READ of size 1 at 0x60b000001549 thread T0
    #0 0x7ffff5e55ccd in wasm::WATParser::Lexer::peek() const /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/lexer.h:137:33
    #1 0x7ffff5e5d5fa in wasm::WATParser::Lexer::takeHexdigit() /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/lexer.h:561:28
    #2 0x7ffff5e59c82 in wasm::WATParser::Lexer::takeStr() /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/lexer.h:905:25
    #3 0x7ffff5e469ab in wasm::WATParser::Lexer::takeString[abi:cxx11]() /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/lexer.h:457:18
    #4 0x7ffff5e43ed4 in wasm::WATParser::ParseDeclsCtx::skipFunctionBody() /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/context-decls.cpp:334:12
    #5 0x7ffff5eb181a in wasm::MaybeResult<wasm::Ok> wasm::WATParser::func<wasm::WATParser::ParseDeclsCtx>(wasm::WATParser::ParseDeclsCtx&) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/parsers.h:3509:19
    #6 0x7ffff5ea5e8c in wasm::MaybeResult<wasm::Ok> wasm::WATParser::modulefield<wasm::WATParser::ParseDeclsCtx>(wasm::WATParser::ParseDeclsCtx&) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/parsers.h:4030:18
    #7 0x7ffff5ea4683 in wasm::Result<wasm::Ok, wasm::Err> wasm::WATParser::moduleBody<wasm::WATParser::ParseDeclsCtx>(wasm::WATParser::ParseDeclsCtx&) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/parsers.h:4071:23
    #8 0x7ffff5ea3df5 in wasm::Result<wasm::Ok, wasm::Err> wasm::WATParser::module<wasm::WATParser::ParseDeclsCtx>(wasm::WATParser::ParseDeclsCtx&) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/parsers.h:4089:3
    #9 0x7ffff5ea3972 in wasm::WATParser::parseModule(wasm::WATParser::ParseDeclsCtx&) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/parse-1-decls.cpp:21:53
    #10 0x7ffff673099b in wasm::WATParser::(anonymous namespace)::doParseModule(wasm::Module&, wasm::WATParser::Lexer&, bool) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/wat-parser.cpp:114:3
    #11 0x7ffff6730409 in wasm::WATParser::parseModule(wasm::Module&, std::basic_string_view<char, std::char_traits<char> >, std::optional<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/wat-parser.cpp:133:10
    #12 0x7ffff6b5d6cd in wasm::readTextData(std::optional<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, wasm::Module&, wasm::IRProfile) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/wasm/wasm-io.cpp:41:21
    #13 0x7ffff6b5d138 in wasm::ModuleReader::readText(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, wasm::Module&) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/wasm/wasm-io.cpp:50:3
    #14 0x7ffff6b5f893 in wasm::ModuleReader::read(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, wasm::Module&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/wasm/wasm-io.cpp:108:5
    #15 0x46174d in main /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/tools/wasm-ctor-eval.cpp:1592:14

0x60b000001549 is located 0 bytes to the right of 105-byte region [0x60b0000014e0,0x60b000001549)
SUMMARY: AddressSanitizer: heap-buffer-overflow /home/new-cases/binaryen/latestest-04.21/binaryen-main/src/parser/lexer.h:137:33 in wasm::WATParser::Lexer::peek() const

Root Cause

Out-of-bounds read in peek() at lexer.h:137 when parsing unterminated/corrupted string literals.
The lexer does not check bounds before reading the next character during escape/hex parsing.

Call chain:

takeString() → takeStr() → takeHexdigit() → peek()

PoC

poc