Security readout for executives and security teams
Plain-English summary
Some Fastify proxy deployments can let an unauthenticated client remove headers that the proxy itself adds before forwarding a request. If those headers drive routing, access control, tenant isolation, or security decisions, upstream services may receive a less-trusted request than intended. The vendor fix is to upgrade the affected packages.
Executive priority
Treat this as urgent for internet-facing Fastify proxy services that rely on added headers for security decisions. The business risk is unauthorized request handling or policy bypass in affected service paths. Patch priority should be high, with exposure triage focused on proxy-to-upstream trust boundaries.
Technical view
@fastify/reply-from <=12.6.1 handles the client Connection header after rewriteRequestHeaders adds proxy headers. Because Connection names hop-by-hop headers, a client can name proxy-added headers and cause them to be stripped before the upstream request. @fastify/http-proxy <=11.4.3 inherits the issue through reply-from. The advisory maps this to CWE-444 and CWE-644 with CVSS 4.0 score 9.0.
Likely exposure
Exposure is likely in Node.js services using Fastify proxy components, especially where rewriteRequestHeaders adds authentication, authorization, routing, tenant, or security headers. Applications not using these packages, not using proxy-added headers, or already upgraded to fixed versions are less likely to be exposed.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. The issue is remotely reachable, unauthenticated, and low complexity, but requires an application context where stripped proxy-added headers affect upstream trust decisions.
Researcher notes
The key validation question is whether upstream services trust headers inserted by the Fastify proxy. Evidence supports header stripping through Connection processing order, but impact depends on application-specific header semantics. Do not assume compromise without logs or telemetry showing relevant missing-header behavior.
Mitigation direction
- Upgrade @fastify/reply-from to v12.6.2 or later.
- Upgrade @fastify/http-proxy to v11.4.4 or later.
- Prioritize services where proxy-added headers influence access control or routing.
- Check vendor advisories for any additional package-specific guidance.
- Redeploy affected services after dependency updates.
Validation and detection
- Inventory package manifests, lockfiles, and SBOMs for affected Fastify packages.
- Identify proxy code using rewriteRequestHeaders to add security-relevant headers.
- Confirm production builds resolve to fixed package versions.
- Review upstream logs for requests missing expected proxy-added headers.
- Regression test that required proxy headers still reach upstream services.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-444: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCWE-644: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-33805 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
2 official scoresWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N——openjsCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N2.25.2redhat-SADPVulnerability scoring details
Base CVSS 4.0 score
9CriticalVector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N
Base CVSS 3.1 score
7.4HighVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- ADP timelineredhat-SADP
Made public.
- CVE publishedCVE Program
The CVE record was published.
- ADP timelineredhat-SADP
Reported to Red Hat.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2026-04-15T11:00:57.611Z: Reported to Red Hat.
- 2026-04-15T10:13:25.147Z: Made public.
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37CVE reference, openjs
- https://cna.openjsf.org/security-advisories.htmlCVE reference, openjs
- https://access.redhat.com/security/cve/CVE-2026-33805CVE reference, redhat-SADP · vdb-entry, x_refsource_REDHAT
- RHBZ#2458651CVE reference, redhat-SADP · issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33805.jsonCVE reference, redhat-SADP · x_sadp-csaf-vex
- https://access.redhat.com/errata/RHSA-2026:10175CVE reference, redhat-SADP · vendor-advisory, x_refsource_REDHAT
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Improper Neutralization of HTTP Headers for Scripting Syntax
Improper Neutralization of HTTP Headers for Scripting Syntax represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.