# CVE-2026-53425: Missing InResponseTo validation in Samly allows acceptance of unsolicited SAML responses > Attackers can hijack user sessions by replaying valid SAML responses because the library fails to validate the InResponseTo field against the original request. - **Severity:** High 7.6 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** A user has to click or open something - **Fix available:** No - **Published:** 20 Aug 2026 - **Updated:** 21 Aug 2026 - **Also known as:** EEF-CVE-2026-53425, GHSA-4mhx-38g6-r4wq ## What is CVE-2026-53425? CVE-2026-53425 is a high-severity authentication bypass vulnerability in dropbox samly, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. ### Official description Insufficient Verification of Data Authenticity vulnerability in dropbox samly allows an attacker to establish an authenticated session using a SAML response the service provider never requested. Samly.SPHandler.validate_authresp/3 in lib/samly/sp_handler.ex validates a SAML response for the SP-initiated flow by comparing only the RelayState value, the IdP identifier, and the presence of a target URL held in the session. It never compares SubjectConfirmationData/@InResponseTo against the ID of the AuthnRequest the service provider issued, and that request ID is never persisted, so no comparison is possible. SAML 2.0 Core section 4.1.4.3 requires a service provider to reject a response whose InResponseTo does not match a request it made. The underlying esaml library checks status, signature, recipient, audience, and staleness, but likewise never inspects InResponseTo, so nothing else closes the gap. Exploitation requires a validly signed assertion from the trusted IdP, which an attacker can obtain for their own account, and a RelayState matching the victim's session; the assertion signature itself remains intact, so this is not a signature-forgery issue. This issue affects samly: from 0.3.0 onward. Weakness: CWE-345 (Insufficient Verification of Data Authenticity) ## Which versions are affected by CVE-2026-53425? 1 open source package ship an affected version, including samly. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `samly` | Hex | From 0.3.0 | None | ## How do I fix CVE-2026-53425? No fix has been published for CVE-2026-53425 yet. Limit exposure of the affected software until one is available. ## Is CVE-2026-53425 being exploited? There is no known exploitation of CVE-2026-53425 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-53425 and fix it if it is affected. What it is: CVE-2026-53425 is a high-severity authentication bypass vulnerability in dropbox samly, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. Exploitation: There is no known exploitation of CVE-2026-53425 in the wild and no public exploit code. Affected packages and fixed versions: - samly (Hex): affected from 0.3.0; no fix listed Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-53425/ (Markdown: https://insights.sbomify.com/CVE-2026-53425/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53425 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53425 - OSV: https://osv.dev/vulnerability/CVE-2026-53425 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-53425/ Summaries are generated and may contain mistakes; the official description above is the record.