CVE-2026-55586
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.
INFO
Published Date :
Aug. 20, 2026, 5:18 p.m.
Last Modified :
Oct. 18, 2026, 8:10 p.m.
Remotely Exploit :
No
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE |
Solution
- Monitor for vendor security advisories.
- Update SumatraPDF to the latest version when available.
- Avoid opening untrusted CHM files.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-55586.
| URL | Resource |
|---|---|
| https://github.com/sumatrapdfreader/sumatrapdf/commit/13b3d4204dd12d93d426f2157b157b149edc29bf | |
| https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-m423-rp8p-whj8 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-55586 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-55586
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-55586 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-55586 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Oct. 18, 2026
Action Type Old Value New Value Added Translation Title: sumatrapdf de sumatrapdfreader, Description: SumatraPDF es un lector multiformato para Windows. En la versión 3.6.1 y anteriores, un archivo CHM manipulado puede suministrar longitudes de código Huffman LZX malformadas a make_decode_table en ext/CHMLib/lzx.c. En la rama de código largo, la función escribe nuevos nodos internos a través de next_symbol antes de validar que la tabla Huffman canónica ha desbordado. El caso PRETREE puede escribir más allá de la tabla PRETREE de 104 entradas en el estado de pila adyacente en la estructura LZXstate cuando se accede a través de chm_open, chm_retrieve_object, LZXdecompress y BUILD_TABLE. Esto produce corrupción de memoria en el montículo en el proceso del analizador, mientras que la ejecución de código arbitrario no ha sido demostrada. No hay una versión corregida disponible a partir de esta revisión. -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 21, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-55586', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-08-21T20:58:52.272523Z'} -
New CVE Received by [email protected]
Aug. 20, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'sumatrapdfreader', 'product': 'sumatrapdf', 'versions': [{'status': 'affected', 'version': '<= 3.6.1rel'}]}] Added 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. Added CVSS V3.1 AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L Added CWE CWE-119 Added CWE CWE-787 Added Reference https://github.com/sumatrapdfreader/sumatrapdf/commit/13b3d4204dd12d93d426f2157b157b149edc29bf Added Reference https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-m423-rp8p-whj8