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CVE-2026-107729— SumatraPDF: Unsigned-to-signed hdrLen validation bypass in SumatraPDF MOBI parsing causes out-of-bounds read

Quick assessment

Affected
sumatrapdfreader sumatrapdf
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

SumatraPDF 是一款面向 Windows 系统的多格式文档阅读器。在版本 3.7.0.22298 中，src/MobiDoc.cpp 对不受信任的无符号字段 mobiHdr.hdrLen 进行验证时，将其窄转换为有符号整数；当该字段值超过 INT_MAX 时，会被转换为负数，从而绕过上限检查。当 EXTH 标志位被设置时，原始无符号值被重新用作指针偏移量，导致 DecodeExthHeader() 函数读取超出记录缓冲区的内存。打开精心构造的 MOBI 文件可可靠地导致应用程序终止，并引发本机访问违规异常；

CVSS 5.5 · Medium

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution
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I. Basic Information for CVE-2026-107729

Vulnerability Information
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Vulnerability Title
SumatraPDF: Unsigned-to-signed hdrLen validation bypass in SumatraPDF MOBI parsing causes out-of-bounds read
Source: CVE Program / CVE List V5
Vulnerability Description
SumatraPDF is a multi-format reader for Windows. In 3.7.0.22298, src/MobiDoc.cpp narrows the untrusted unsigned mobiHdr.hdrLen field to a signed integer for validation; values above INT_MAX become negative and bypass the upper-bound check. When the EXTH flag is set, the original unsigned value is reused as a pointer offset, causing DecodeExthHeader() to read beyond the record buffer. Opening a crafted MOBI file can reliably terminate the application with a native access violation; no code execution, information disclosure, or integrity impact has been demonstrated. No fixed version is available as of this review.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存读
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
sumatrapdfreader sumatrapdf <= 3.7.0.22298 -

II. Public POCs for CVE-2026-107729

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III. Intelligence Information for CVE-2026-107729

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Other References for CVE-2026-107729 (2)

Same Patch Batch · sumatrapdfreader · 2026-10-08 · 11 CVEs total

CVE-2026-107732 8.4 HIGH SumatraPDF: Markup/command-link injection into UI notification text
CVE-2026-107734 7.1 HIGH SumatraPDF: SyncTeX Argument Injection in Inverse Search Enables Arbitrary Command Executi
CVE-2026-107802 7.1 HIGH SumatraPDF — Windows command-line argument injection in AI selection-translate
CVE-2026-107733 6.8 MEDIUM SumatraPDF: Null-pointer dereference in `CmdExec` when no document tab is open
CVE-2026-107736 6.8 MEDIUM SumatraPDF: stack buffer overflow while processing EXIF Orientation metadata
CVE-2026-107738 6.8 MEDIUM SumatraPDF: Untrusted binary record offset used without lower-bound validation
CVE-2026-107737 5.7 MEDIUM SumatraPDF CHM `its://` signed index causes an out-of-bounds object lookup
CVE-2026-107731 5.5 MEDIUM SumatraPDF: LIT parser range-validation flaws cause invalid-pointer reads and denial of se
CVE-2026-107730 5.5 MEDIUM SumatraPDF: Signed integer overflow in the LIT header parsing causes invalid-pointer read
CVE-2026-107735 5.4 MEDIUM SumatraPDF: `sumatrapdfrestrict.ini` never revokes any permission (fail-open policy initia

IV. Related Vulnerabilities

Same product: sumatrapdf
Same vendor: sumatrapdfreader
Same weakness: CWE-125

V. Comments for CVE-2026-107729

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