CVE-2026-58055Public exploitNetwork attack vector

Cross-client response poisoning via Upgrade body forwarding

Published Jun 28, 2026 · Updated Jun 28, 2026

HTTP request smuggling in nghttp2 nghttpx through 1.69.0 allows remote attackers to poison cross-client response queues. The HTTP/1.1 frontend forwarding path accepts Upgrade requests with Content-Length, re-adds hop-by-hop Upgrade and Connection headers, and streams the body to a reusable HTTP/1.1 backend connection. Exploitation requires an Upgrade-aware backend that leaves the body bytes to be parsed as another request, enabling attacker-selected responses to be delivered to subsequent clients.

CVSS severity6.3
Medium
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in nghttp2 nghttpx through 1.69.0 allows remote attackers to poison cross-client response queues. The HTTP/1.1 frontend forwarding path accepts Upgrade requests with Content-Length, re-adds hop-by-hop Upgrade and Connection headers, and streams the body to a reusable HTTP/1.1 backend connection. Exploitation requires an Upgrade-aware backend that leaves the body bytes to be parsed as another request, enabling attacker-selected responses to be delivered to subsequent clients.

The record

CVE
CVE-2026-58055
Published
Jun 28, 2026
Updated
Jun 28, 2026
Vendor
nghttp2
Product
nghttp2
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=1.69.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

nghttp2 · nghttp2version=0 <=1.69.0

Published CVSS scores

6.8VulnCheckCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
6.3VulnCheckCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:L/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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