# CVE-2026-73495: blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass) > Attackers can bypass proxy header sanitization by injecting headers via HTTP chunked trailers, spoofing IPs or authorization in http4s applications. - **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 12 Aug 2026 - **Updated:** 13 Aug 2026 - **Also known as:** GHSA-46q4-43ph-c6fr ## What is CVE-2026-73495? CVE-2026-73495 is a high-severity vulnerability in http4s blaze, published on 12 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description blaze is a Scala library for building asynchronous pipelines, with a focus on network IO. Prior to 0.23.18 and 1.0.0-M42, blaze-server can merge HTTP/1.1 chunked-body trailer fields into Request.headers. Because trailer fields are attacker-controlled, an unauthenticated remote client can inject arbitrary header names and values, including X-Forwarded-For and internal authorization headers, that a fronting proxy sanitized from the request-header section, bypassing header-based trust decisions in the application. Any http4s application using BlazeServerBuilder over HTTP/1.1 whose routes or middleware trust proxy-set headers, including X-Forwarded-For, X-Real-IP, and X-Forwarded-Host, is affected. If a fronting proxy strips or normalizes those headers but forwards chunked bodies with trailers intact, an attacker can spoof client IP for allow-lists, rate limits, or auditing, forge the https scheme, or inject internal authorization headers. A promoted Connection: close trailer is also honored, allowing attacker-controlled termination of pooled backend connections. This issue is fixed in versions 0.23.18 and 1.0.0-M42. Weakness: CWE-444 (Inconsistent Interpretation of HTTP Requests) ## Which versions are affected by CVE-2026-73495? 10 open source packages ship an affected version, including org.http4s:blaze-http_2.13, org.http4s:blaze-http_2.12 and org.http4s:blaze-http_3. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `org.http4s:blaze-http_2.13` | Maven | All versions | 0.23.18 | | `org.http4s:blaze-http_2.13` | Maven | All versions | 0.23.18 | | `org.http4s:blaze-http_2.13` | Maven | From 1.0.0-M1 | 1.0.0-M42 | | `org.http4s:blaze-http_2.13` | Maven | From 1.0.0-M1 | 1.0.0-M42 | | `org.http4s:blaze-http_2.12` | Maven | All versions | 0.23.18 | | `org.http4s:blaze-http_2.12` | Maven | All versions | 0.23.18 | | `org.http4s:blaze-http_3` | Maven | All versions | 0.23.18 | | `org.http4s:blaze-http_3` | Maven | All versions | 0.23.18 | | `org.http4s:blaze-http_3` | Maven | From 1.0.0-M1 | 1.0.0-M42 | | `org.http4s:blaze-http_3` | Maven | From 1.0.0-M1 | 1.0.0-M42 | ## How do I fix CVE-2026-73495? Upgrade org.http4s:blaze-http_2.13 to a fixed version for your release line: 0.23.18 or 1.0.0-M42. ## Is CVE-2026-73495 being exploited? There is no known exploitation of CVE-2026-73495 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-73495 and fix it if it is affected. What it is: CVE-2026-73495 is a high-severity vulnerability in http4s blaze, published on 12 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-73495 in the wild and no public exploit code. Affected packages and fixed versions: - org.http4s:blaze-http_2.13 (Maven): affected all versions; fixed in 0.23.18 - org.http4s:blaze-http_2.13 (Maven): affected all versions; fixed in 0.23.18 - org.http4s:blaze-http_2.13 (Maven): affected from 1.0.0-M1; fixed in 1.0.0-M42 - org.http4s:blaze-http_2.13 (Maven): affected from 1.0.0-M1; fixed in 1.0.0-M42 - org.http4s:blaze-http_2.12 (Maven): affected all versions; fixed in 0.23.18 - org.http4s:blaze-http_2.12 (Maven): affected all versions; fixed in 0.23.18 - org.http4s:blaze-http_3 (Maven): affected all versions; fixed in 0.23.18 - org.http4s:blaze-http_3 (Maven): affected all versions; fixed in 0.23.18 - org.http4s:blaze-http_3 (Maven): affected from 1.0.0-M1; fixed in 1.0.0-M42 - org.http4s:blaze-http_3 (Maven): affected from 1.0.0-M1; fixed in 1.0.0-M42 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-2026-73495/ (Markdown: https://insights.sbomify.com/CVE-2026-73495/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-73495 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-73495 - OSV: https://osv.dev/vulnerability/CVE-2026-73495 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-73495/ Summaries are generated and may contain mistakes; the official description above is the record.