Is CVE-2026-115758 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-115758 being exploited in the wild.

How severe is CVE-2026-115758?

Informational severity, published 4 November 2026.

How is CVE-2026-115758 attacked?

It is attacked over the network or from the adjacent network, in a software library.

Am I affected by CVE-2026-115758?

Check whether you run SumatraPDF at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-115758: SumatraPDF TLS hostname validation bypass in HttpGet

CVE-2026-115758 · Severity: info · Published 2026-11-04

SumatraPDF is a document reader for Windows that automatically checks for updates. The application disables SSL/TLS hostname verification, allowing a network attacker with any trusted certificate to intercept update checks and inject malicious promotional text or links directly into the application interface, or serve forged crash-symbol archives. Installer replacement is prevented by additional validation, but user data and experience are at risk.

Technologies: SumatraPDF. Vendors: SumatraPDF.

Quick answers

Is CVE-2026-115758 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-115758 being exploited in the wild.
How severe is CVE-2026-115758?: Informational severity, published 4 November 2026.
Which products and versions are affected?: SumatraPDF 3.6.1 and earlier.
Is there a fix for CVE-2026-115758?: No fixed version is recorded yet. Restrict SumatraPDF's network access to trusted networks, or use a firewall rule to block outbound connections to sumatrapdfreader.org unless the update check is user-initiated and verified. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-115758 attacked?: It is attacked over the network or from the adjacent network, in a software library.
Am I affected by CVE-2026-115758?: Check whether you run SumatraPDF at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

Restrict SumatraPDF's network access to trusted networks, or use a firewall rule to block outbound connections to sumatrapdfreader.org unless the update check is user-initiated and verified.

Technical details

HttpGet() in src/base/Http_win.cpp unconditionally sets INTERNET_FLAG_IGNORE_CERT_CN_INVALID, disabling hostname matching while retaining certificate-chain validation (CWE-297). A network-positioned attacker with a Windows-trusted certificate for an attacker-controlled domain can intercept HTTPS requests to the update-check and crash-symbol endpoints; parsed promo text is applied before validation gates, enabling injection of attacker-controlled URLs into the UI, and crash-symbol extraction processes untrusted archive data. The commit bd30134 removes the flag and adds user-facing error dialogs on manual update-check failures.

Affected products

SumatraPDF SumatraPDF 3.6.1 and earlier

Timeline

2026-07-29: disclosed
2026-11-04: advisory

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.