CVE-2026-23951VulnerabilityPublished 22 Jan 2026

CVE-2026-23951: sumatrapdfreader sumatrapdf · Out-of-bounds Read

Affects sumatrapdfreader sumatrapdfSource CVE Database V5

Not known to be exploited · CVSS 5.5 Medium.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

5.5Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 12% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Attack Vector: Local
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 22 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
sumatrapdfreadersumatrapdf	Affected <=3.5.2rel	Fixed in–
GitHubsumatrapdfreader/sumatrapdf`pkg:github/sumatrapdfreader/sumatrapdf`Other threats	Affected–	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

1. Avoid opening Mobi files from untrusted or unknown sources until a patch is released. 2. Implement strict email and file filtering policies to block or quarantine suspicious Mobi files. 3. Educate users about the risks of opening unsolicited or unexpected eBook files, emphasizing caution with Mobi format files. 4. Monitor SumatraPDF usage within the organization and consider restricting its use or replacing it with alternative PDF/eBook readers that are not vulnerable. 5. Employ application whitelisting and sandboxing to limit the impact of crashes and prevent potential exploitation attempts. 6. Regularly check for vendor updates or security advisories to apply patches promptly once available. 7. Use endpoint detection and response (EDR) tools to detect abnormal application crashes or suspicious file access patterns related to SumatraPDF. 8. Maintain backups and incident response plans to quickly recover from potential denial of service incidents.

Description

CVE-2026-23951 is a medium severity vulnerability in SumatraPDF (versions up to 3.5.2rel) caused by an off-by-one error in PalmDbReader::GetRecord when processing crafted Mobi files. This leads to an integer underflow during size calculation, resulting in an out-of-bounds heap read that crashes the application. Exploitation requires local access and user interaction to open a malicious file, with no impact on confidentiality or integrity, only availability. No patches are currently available, and no known exploits exist in the wild. European organizations using SumatraPDF for document reading may experience denial of service if targeted. Mitigation involves avoiding opening untrusted Mobi files and monitoring for updates from the vendor. Countries with higher usage of SumatraPDF and significant document handling needs, such as Germany, France, and the UK, are most likely to be affected.

Impact

For European organizations, the primary impact of CVE-2026-23951 is denial of service due to application crashes when opening malicious Mobi files. This can disrupt workflows, especially in environments where SumatraPDF is used extensively for document reading or eBook processing, such as publishing houses, libraries, educational institutions, and legal firms. Although the vulnerability does not lead to data breaches or code execution, repeated crashes could lead to productivity loss and potential operational disruptions. Organizations relying on automated document processing or user environments where untrusted files might be opened are at higher risk. Since no known exploits are in the wild, the immediate threat is low, but the absence of patches means the vulnerability remains exploitable if attackers develop payloads. The requirement for user interaction limits remote exploitation but does not eliminate risk in scenarios involving phishing or malicious file distribution. The impact on availability could also affect business continuity if critical users or systems are targeted.

CWE-125Out-of-bounds Read (opens in a new tab)
Base weaknessCWE Top 25 (2025): #8
The product reads data past the end, or before the beginning, of the intended buffer.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Architecture and Design · Language Selection
Use a language that provides appropriate memory abstractions.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Overread Buffers (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-191Integer Underflow (Wrap or Wraparound) (opens in a new tab)
Base weakness
The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 29 Jan 2026, 08:41 UTC

WeaknessesCWE-125, CWE-191

Technical details

References

Community reviews

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