CVE-2026-55603: Chimurai Http-proxy-middleware vulnerability (CVSS 7.5)

Description

http-proxy-middleware is node.js http-proxy middleware. From 3.0.4 until 3.0.7 and 4.1.1, fixRequestBody() is the library's documented helper for re-emitting a request body that was already consumed by a body parser. When the outgoing Content-Type is multipart/form-data, it rebuilds the body with handlerFormDataBodyData(), which interpolates each req.body key and value directly into the multipart wire format without neutralizing CR/LF. A \r\n inside a value (or key) lets an attacker close the current part and inject an entirely new form part. Because the proxy's own body parser saw a single opaque value, any gateway-side policy or validation performed on req.body is evaluated against a different set of fields than the upstream backend ultimately parses a request/parameter desynchronization across the trust boundary. This vulnerability is fixed in 3.0.7 and 4.1.1.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityHigh

Privileges requiredNone

User interactionNone

ScopeChanged

ConfidentialityLow

IntegrityHigh

AvailabilityNone

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N

Affected products

Chimurai Http-proxy-middleware≥ 3.0.4 < 3.0.7 · ≥ 4.0.0 < 4.1.1

Remediation

Fixed in

Chimurai Http-proxy-middleware≥ 3.0.7

Patch & vendor advisories

https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-gcq2-9pq2-cxqm

References

https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-gcq2-9pq2-cxqmExploitMitigationVendor Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-55603 being actively exploited?

CVE-2026-55603 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.29%.

How severe is CVE-2026-55603?

CVE-2026-55603 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.29% probability of exploitation.

Which products are affected by CVE-2026-55603?

Affected products include Chimurai Http-proxy-middleware.

How do I fix CVE-2026-55603?

Upgrade affected software to a fixed version, for example Chimurai Http-proxy-middleware 3.0.7 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-55603 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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