{"id":"CVE-2026-55586","aliases":["EUVD-2026-63469","GHSA-m423-rp8p-whj8"],"status":"published","title":"SumatraPDF: Heap out-of-bounds write in vendored CHMLib LZX Huffman table construction reachable from crafted CHM files","description":"SumatraPDF is a multi-format reader for Windows. In 3.6.1 and earlier, a crafted CHM file can supply malformed LZX Huffman code lengths to make_decode_table in ext/CHMLib/lzx.c. In the long-code branch, the function writes new internal nodes through next_symbol before validating that the canonical Huffman table has overflowed. The PRETREE case can write beyond the 104-entry PRETREE_table into adjacent heap state in struct LZXstate when reached through chm_open, chm_retrieve_object, LZXdecompress, and BUILD_TABLE. This produces heap memory corruption in the parser process, while arbitrary code execution has not been demonstrated. No fixed version is available as of this review.","severity":{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00174,"percentile":0.06935,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-119","CWE-787"],"published":"2026-08-20T16:35:07Z","modified":"2026-10-28T11:09:57Z","products":[{"vendor":"sumatrapdfreader","product":"sumatrapdf"}],"references":[{"url":"https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-m423-rp8p-whj8","tags":["x_refsource_CONFIRM","advisory"]},{"url":"https://github.com/sumatrapdfreader/sumatrapdf/commit/13b3d4204dd12d93d426f2157b157b149edc29bf","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55586.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55586","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-55586","title":"SumatraPDF: Heap out-of-bounds write in vendored CHMLib LZX Huffman table construction reachable from crafted CHM files","description":"SumatraPDF is a multi-format reader for Windows. In 3.6.1 and earlier, a crafted CHM file can supply malformed LZX Huffman code lengths to make_decode_table in ext/CHMLib/lzx.c. In the long-code branch, the function writes new internal nodes through next_symbol before validating that the canonical Huffman table has overflowed. The PRETREE case can write beyond the 104-entry PRETREE_table into adjacent heap state in struct LZXstate when reached through chm_open, chm_retrieve_object, LZXdecompress, and BUILD_TABLE. This produces heap memory corruption in the parser process, while arbitrary code execution has not been demonstrated. No fixed version is available as of this review.","status":"published","published":"2026-08-20T16:35:07.359Z","modified":"2026-08-21T21:47:17.24Z","cvss":[{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L","level":"medium","assessor":"cna"}],"cwes":["CWE-119","CWE-787"],"updated_at":"2026-11-02T14:20:12.260247Z"}],"euvd":[{"id":"EUVD-2026-63469","description":"SumatraPDF is a multi-format reader for Windows. In 3.6.1 and earlier, a crafted CHM file can supply malformed LZX Huffman code lengths to make_decode_table in ext/CHMLib/lzx.c. In the long-code branch, the function writes new internal nodes through next_symbol before validating that the canonical Huffman table has overflowed. The PRETREE case can write beyond the 104-entry PRETREE_table into adjacent heap state in struct LZXstate when reached through chm_open, chm_retrieve_object, LZXdecompress, and BUILD_TABLE. This produces heap memory corruption in the parser process, while arbitrary code execution has not been demonstrated. No fixed version is available as of this review.","status":"published","published":"2026-08-20T16:35:07Z","modified":"2026-08-21T21:47:17Z","cvss":[{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L","level":"medium"}],"updated_at":"2026-11-02T18:01:36.505605Z"}],"nvd":[{"id":"CVE-2026-55586","description":"SumatraPDF is a multi-format reader for Windows. In 3.6.1 and earlier, a crafted CHM file can supply malformed LZX Huffman code lengths to make_decode_table in ext/CHMLib/lzx.c. In the long-code branch, the function writes new internal nodes through next_symbol before validating that the canonical Huffman table has overflowed. The PRETREE case can write beyond the 104-entry PRETREE_table into adjacent heap state in struct LZXstate when reached through chm_open, chm_retrieve_object, LZXdecompress, and BUILD_TABLE. This produces heap memory corruption in the parser process, while arbitrary code execution has not been demonstrated. No fixed version is available as of this review.","status":"published","published":"2026-08-20T17:18:27.723Z","modified":"2026-10-18T20:10:00.11Z","cvss":[{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L","level":"medium","assessor":"secondary"}],"cwes":["CWE-119","CWE-787"],"updated_at":"2026-11-02T14:12:40.302911Z"}],"osv":[{"id":"CVE-2026-55586","title":"SumatraPDF: Heap out-of-bounds write in vendored CHMLib LZX Huffman table construction reachable from crafted CHM files","description":"SumatraPDF is a multi-format reader for Windows. In 3.6.1 and earlier, a crafted CHM file can supply malformed LZX Huffman code lengths to make_decode_table in ext/CHMLib/lzx.c. In the long-code branch, the function writes new internal nodes through next_symbol before validating that the canonical Huffman table has overflowed. The PRETREE case can write beyond the 104-entry PRETREE_table into adjacent heap state in struct LZXstate when reached through chm_open, chm_retrieve_object, LZXdecompress, and BUILD_TABLE. This produces heap memory corruption in the parser process, while arbitrary code execution has not been demonstrated. No fixed version is available as of this review.","status":"published","published":"2026-08-20T16:35:07.359Z","modified":"2026-10-28T11:09:57.808487264Z","cvss":[{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L","level":"medium"}],"cwes":["CWE-119","CWE-787"],"updated_at":"2026-11-02T15:45:11.22012Z"}]}}