Security readout for executives and security teams
Plain-English summary
A crafted Mobi file can crash SumatraPDF on Windows when opened by a user. The issue is in Palm database parsing and affects availability, not data theft or tampering per the CVSS record. No published fix is listed in the provided sources, so business urgency depends on how widely SumatraPDF handles untrusted documents.
Executive priority
Treat as a moderate endpoint availability issue. Prioritize environments where SumatraPDF is broadly deployed or users routinely open external e-book/document files. It is not currently evidenced as exploited, and the cited impact is application crash only.
Technical view
CVE-2026-23951 is an off-by-one validation bug in PalmDbReader::GetRecord. With exactly two records, size calculation can integer-underflow, causing an out-of-bounds heap read and application crash when opening a crafted Mobi file. Reported impact maps to CWE-125 and CWE-191, CVSS 3.1 score 5.5, local attack vector, user interaction required.
Likely exposure
Exposure is most likely on Windows endpoints running SumatraPDF up to 3.5.2rel, especially where users open Mobi files from email, downloads, tickets, or external partners. Systems that do not use SumatraPDF or do not handle Mobi files have lower practical exposure.
Exploitation context
The source bundle does not report active exploitation, and the CVE is not marked KEV. Exploitation requires convincing a user to open a crafted Mobi file locally. The documented result is a crash, creating denial-of-service risk rather than confidentiality or integrity impact.
Researcher notes
Evidence is limited to the CVE record, GitHub advisory, and referenced source file. The advisory states no published fixes at publication time. Avoid assuming memory disclosure or code execution; the provided CVSS impact lists confidentiality and integrity as none, availability high.
Mitigation direction
- Check SumatraPDF vendor advisory for updated fixed versions or official workarounds.
- Limit opening Mobi files from untrusted sources until vendor guidance is available.
- Consider alternative readers for Mobi files in high-risk workflows.
- Use endpoint controls to restrict untrusted document handling where feasible.
- Inventory SumatraPDF installations and prioritize exposed user groups.
Validation and detection
- Identify endpoints with SumatraPDF installed and record version numbers.
- Confirm whether versions are 3.5.2rel or earlier.
- Review workflows where users receive or open Mobi files.
- Check the GitHub advisory for fix status before remediation decisions.
- Monitor CVE and vendor pages for updates.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-125: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCWE-191: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-23951 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-hj4w-c5x8-p2hvCVE reference · x_refsource_CONFIRM
- https://github.com/sumatrapdfreader/sumatrapdf/blob/master/src/PalmDbReader.cppCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Out-of-bounds Read
Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Integer Underflow (Wrap or Wraparound)
Integer Underflow (Wrap or Wraparound) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.