CVERadar
HIGH · CVSS 3.1 7.5Exploit-DBEPSS 0.48% (p41)Threat level 45

CVE-2026-25961: CVE-2026-25961: SumatraPDF is a multi-format reader for Windows. In 3.5.0 through 3.5.2, SumatraPDF's upda…

sumatrapdfreader · sumatrapdf · NVD published 2026-02-10 · posted 2026-04-30 · last modified 2026-06-17

What it is

SumatraPDF is a multi-format reader for Windows. In 3.5.0 through 3.5.2, SumatraPDF's update mechanism disables TLS hostname verification (INTERNET_FLAG_IGNORE_CERT_CN_INVALID) and executes installers without signature checks. A network attacker with any valid TLS certificate (e.g., Let's Encrypt) can intercept the update check request, inject a malicious installer URL, and achieve arbitrary code execution.

WeaknessCWE-295CWE-494
CVSS vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H (source: [email protected])
ATT&CK tacticsCredential Access → Collection

Exploitation evidence

First exploit evidence seen: 2026-04-30 (earliest date across the sources below).

Exploited in the wild

No source on this site lists in-the-wild exploitation yet (CISA KEV, VulnCheck KEV).

Public exploit code

Exploit-DB

  • EDB-52535: SumatraPDF 3.5.2 - Remote Code Execution (2026-04-30)

GitHub proof-of-concept repositories below quality bar

1 public repositories from 1 accounts, first seen 2026-02-10.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: Exploit-DB (OffSec) · nomi-sec/PoC-in-GitHub.

Defend the Chain

The attack chain for CVE-2026-25961 laid across the MITRE ATT&CK Enterprise tactics. Solid cards come from the MITRE CTID KEV mappings; dashed cards are inferred by CVERadar from the CWE or description. Correct defences are real ATT&CK mitigations for that technique.

Threat level 45/100
Defender level 1 · 0 XP
Chain links broken: 0/1

Reconnaissance

Resource Development

Initial Access

Execution

Persistence

Privilege Escalation

Stealth

Defense Impairment

Credential Access

Discovery

Lateral Movement

Collection

Command and Control

Exfiltration

Impact

Pick a red technique card on the board, then choose the defence that stops it.

Defend against T1557 Adversary-in-the-Middle Inferred

Inferred from CWE CWE-295

How to fix it

Fixed versions

  • sumatrapdfreader sumatrapdf: versions up to and including 3.5.2 are affected; check the vendor advisory for the fixed release.

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

MITRE ATT&CK mitigations for this chain

  • M1037 Filter Network Traffic (for T1557) : Use network appliances and host-based security software to block network traffic that is not necessary within the environment, such as legacy protocols that may be leveraged for AiTM conditions.
  • M1041 Encrypt Sensitive Information (for T1557) : Ensure that all wired and/or wireless traffic is encrypted appropriately. Use best practices for authentication protocols, such as Kerberos, and ensure web traffic that may contain credentials is protected by SSL/TLS.
  • M1035 Limit Access to Resource Over Network (for T1557) : Limit access to network infrastructure and resources that can be used to reshape traffic or otherwise produce AiTM conditions.
  • M1042 Disable or Remove Feature or Program (for T1557) : Disable legacy network protocols that may be used to intercept network traffic if applicable, especially those that are not needed within an environment.
  • M1017 User Training (for T1557) : Train users to be suspicious about certificate errors. Adversaries may use their own certificates in an attempt to intercept HTTPS traffic. Certificate errors may arise when the application’s certificate does not match the one expected by the host.
  • M1031 Network Intrusion Prevention (for T1557) : Network intrusion detection and prevention systems that can identify traffic patterns indicative of AiTM activity can be used to mitigate activity at the network level.
  • M1030 Network Segmentation (for T1557) : Network segmentation can be used to isolate infrastructure components that do not require broad network access. This may mitigate, or at least alleviate, the scope of AiTM activity.

Detection Generic guidance

  • Credential Access: Monitor for credential dumping, unusual LSASS access and sudden authentication from new sources.
  • Collection: Watch for bulk reads of databases, file shares or mailboxes by the affected service.

Response checklist Generic guidance

  1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
  2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
  3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
  4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.

Sources