Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:HSummary
CVE-2026-25961 is a high-severity Improper Certificate Validation (CWE-295) vulnerability in Sumatrapdfreader Sumatrapdf. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Supply Chain Compromise (T1195); ranked at the 37th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to CM-14 (Signed Components) and SC-17 (Public Key Infrastructure Certificates) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-25961 affects SumatraPDF, a multi-format reader for Windows, specifically versions 3.5.0 through 3.5.2. The vulnerability lies in the application's update mechanism, which disables TLS hostname verification by using the INTERNET_FLAG_IGNORE_CERT_CN_INVALID flag and executes downloaded installers without performing signature checks. This issue, published on 2026-02-09, is associated with CWE-295 (Improper Certificate Validation) and CWE-494 (Download of Code Without Integrity Check), earning a CVSS v3.1 base score of 7.5 (AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H).
A network-based attacker positioned to perform a man-in-the-middle interception can exploit this vulnerability if they possess any valid TLS certificate, such as one issued by Let's Encrypt. By intercepting the update check request from a victim user, the attacker can inject a malicious installer URL. If the user interacts with the update process (UI:R), the application will download and execute the malicious installer, resulting in arbitrary code execution on the victim's Windows system with the user's privileges.
Mitigation details and patches are outlined in the official GitHub security advisory at https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-xpm2-rr5m-x96q.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-6869
Vulnerability Data
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…
more
check request, inject a malicious installer URL, and achieve arbitrary code execution.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 21 hardening rules · 5 OS baselines
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Mitigating Controls (NIST 800-53 r5) AI
Requires digital signature verification before component installation, directly stopping execution of code downloaded without integrity checks.
PKI certificate issuance and acquisition under an approved policy establishes the trusted roots and processes needed for correct validation.
Employs integrity verification tools that can identify missing or failed checks on downloaded software after the fact.
Protecting session authenticity depends on cryptographic mechanisms whose trust depends on correct certificate validation.
Requiring confidentiality and integrity protection of transmitted data drives use of properly validated certificates in protocols such as TLS.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Directly requires assessing authenticity/integrity of software before acquisition and use, preventing unverified downloads.
Certificate-based authentication of users/services/hardware directly depends on correct validation.
Proper certificate validation is a core mechanism for protecting data-in-transit confidentiality and integrity.
Prevents execution of unauthorized software, blocking the outcome of an unchecked download.
Secure development practices explicitly include implementing correct certificate validation logic.
Identity assertions conveyed via certificates require validation to be verified.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Mandating integrity checks, digital signatures, and origin tracing for ICT components directly reduces the chance that code or firmware lacking an integrity check will be accepted into the organisation’s environment.
Requiring issuance and validation of public-key certificates under an approved policy reduces the chance that certificates with improper validation will be trusted.
Requiring suppliers to disclose vulnerabilities and mandating verified updates lowers the chance that code lacking integrity checks will be deployed.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (3 rules)
- V-248574 YUM must be configured to prevent the installation of patches, service packs, device drivers, or OL 8 system components that have not been digitally signed using a certificate that is recognized and approved by the organization. prevents CWE-295
- V-248531 OL 8, for PKI-based authentication, must validate certificates by constructing a certification path (which includes status information) to an accepted trust anchor. prevents CWE-295
- V-248575 OL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-295, CWE-494
Oracle Linux 9 (1 rule)
- V-271524 OL 9 must check the GPG signature of software packages originating from external software repositories before installation. prevents CWE-494
RHEL 7 (2 rules)
- V-204447 The Red Hat Enterprise Linux operating system must prevent the installation of software, patches, service packs, device drivers, or operating system components from a repository without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-295, CWE-494
- V-204448 The Red Hat Enterprise Linux operating system must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-295, CWE-494
RHEL 8 (2 rules)
- V-230264 RHEL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components from a repository without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-295, CWE-494
- V-230265 RHEL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-295
RHEL 9 (1 rule)
- V-257820 RHEL 9 must check the GPG signature of software packages originating from external software repositories before installation. prevents CWE-494