Home/CVE/Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the
CVE
CVE-2026-52845
Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the
Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the exact client-supplied identity header before copying the trusted value from the auth gateway. But when the request later goes through php_fastcgi, Caddy normalizes HTTP headers into CGI variables by replacing - with _.
This lets a client send an underscore alias that survives the forward_auth delete step but becomes the same PHP/FastCGI variable. Result: a remote client can inject or sometimes override identity/group headers trusted by PHP/FastCGI applications behind Caddy. This vulnerability is fixed in 2.11.4.
HIGH · CVSS 8.1
Schedule remediation
- CVSS base score ≥ 7.0
No Sigma yet — build one →
YARA rules0
Look this up elsewhere - one-click external pivots
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How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2026-52845, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.
Triage: should I act now? Four signals, and they are not interchangeable:
CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked.
EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal.
CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score.
Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.
How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.
Then what - two workflows:
Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits.
PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.
Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).
EPSS exploitation probability
n/a
No EPSS score in our data for this CVE. EPSS is published daily for scored CVEs - a very new, reserved, or rejected CVE may not have one yet.
CVSS metric silhouette
shape grows toward worst-case
SSVC triage
No SSVC vulnrichment for this CVE. CISA's Vulnrichment program scores newer CVEs (~2024 onwards) plus selected older critical ones. Use the EPSS probability + KEV status to triage instead.
CVSS vector breakdown
Exploitability - how they get in
Attack Vector
Network
Adjacent
Local
Physical
Attack Complexity
Low
High
Privileges Required
None
Low
High
User Interaction
None
Required
Scope
Unchanged
Changed
Impact - what breaks
Confidentiality
None
Low
High
Integrity
None
Low
High
Availability
None
Low
High
VECTOR
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N◆
ATT&CK techniques
8Techniques this CVE enables. Pills with a solid outline are high confidence - named directly in ATT&CK or Nuclei, or human-curated by CTID; the rest are inferred from the weakness type using MITRE's CVE Mapping Methodology and the CWE → CAPEC chain. Broad, generic-weakness guesses are filtered out. A small N× marks a technique that N independent sources agree on.
T1036.001 · Invalid Code Signature T1134 · Access Token Manipulation T1134.001 · Token Impersonation/Theft T1528 · Steal Application Access Token T1539 · Steal Web Session Cookie T1550.004 · Web Session Cookie T1553.002 · Code Signing T1557 · Adversary-in-the-Middle
▤ Build a SIEM detection for these techniques
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CAPEC attack patterns
12Attack patterns this CVE enables - the bridge from weakness to ATT&CK technique.
CAPEC-CAPEC-114 · Authentication Abuse CAPEC-CAPEC-115 · Authentication Bypass CAPEC-CAPEC-151 · Identity Spoofing CAPEC-CAPEC-194 · Fake the Source of Data CAPEC-CAPEC-21 · Exploitation of Trusted Identifiers CAPEC-CAPEC-22 · Exploiting Trust in Client CAPEC-CAPEC-273 · HTTP Response Smuggling CAPEC-CAPEC-33 · HTTP Request Smuggling CAPEC-CAPEC-459 · Creating a Rogue Certification Authority Certificate CAPEC-CAPEC-461 · Web Services API Signature Forgery Leveraging Hash Function Extension Weakness CAPEC-CAPEC-473 · Signature Spoof CAPEC-CAPEC-476 · Signature Spoofing by Misrepresentation
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Weakness Classification
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Affected Packages
2Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
Go
github.com/caddyserver/caddy
HIGH
Go
github.com/caddyserver/caddy/v2
HIGH
fixed in 2.11.4
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Related CVEs
8CVEs linked to this one by a shared weakness (CWE) or affected product - joins on data already in the engine, with the reason shown per row.
CVE-1999-0366
In some cases, Service Pack 4 for Windows NT 4.0 can allow access to network sha...
same CWE-287
CVE-1999-0680
Windows NT Terminal Server performs extra work when a client opens a new connect...
same CWE-287
CVE-1999-0987
Windows NT does not properly download a system policy if the domain user logs in...
same CWE-287
CVE-2001-0537
HTTP server for Cisco IOS 11.3 to 12.2 allows attackers to bypass authentication...
5
same CWE-287
CVE-1999-0012
Some web servers under Microsoft Windows allow remote attackers to bypass access...
same CWE-290
HIGH
CVE-2009-1048
The web interface on the snom VoIP phones snom 300, snom 320, snom 360, snom 370...
same CWE-290
CRITICAL
CVE-2013-5661
Cache Poisoning issue exists in DNS Response Rate Limiting.
same CWE-290
MEDIUM
CVE-2017-6405
An issue was discovered in Veritas NetBackup 8.0 and earlier and NetBackup Appli...
same CWE-290
HIGH
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References & Sources
1Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.