Summary
A service for building customized OS artifacts, such as VM images and OSTree commits, that uses osbuild under the hood. Besides building images for local usage, it can also upload images directly to cloud. It is compatible with composer-cli and cockpit-composer clients.
Security Fix(es):
* net/mail: golang: net/mail: Denial of Service via pathological email address parsing (CVE-2026-42499)
* net/mail: golang: Go net/mail: Denial of Service via crafted email inputs (CVE-2026-39820)
* golang.org/x/net/idna: golang: net/[http:](http:) golang.org/x/net/idna: Privilege escalation via incorrect Punycode label processing (CVE-2026-39821)
* mime: golang: Golang MIME: Denial of Service via maliciously-crafted MIME header (CVE-2026-42504)
* encoding/asn1: golang: Go encoding/asn1: Denial of Service via excessive recursion in Unmarshal (CVE-2026-33818)
* net/url: golang: golang net/url: Denial of Service from quadratic complexity in path resolution (CVE-2026-56860)
* net/[http:](http:) golang: Go net/[http:](http:) Unencrypted HTTP/2 connections vulnerable to Denial of Service (CVE-2026-56853)
* html/template: golang: Go html/template: Cross-Site Scripting via pathological input (CVE-2026-56858)
* crypto/tls: golang: Golang crypto/tls: Denial of Service via indefinite KeyUpdate messages (CVE-2026-56862)
* encoding/xml: golang: Go: Denial of Service via XML decoding recursion depth issue (CVE-2026-56859)
For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.
Fixed packages 3
| Release | Package | Fixed in |
|---|---|---|
| AlmaLinux · 9 | osbuild-composer | 165.1-4.el9_8.1.alma.1 |
| AlmaLinux · 9 | osbuild-composer-core | 165.1-4.el9_8.1.alma.1 |
| AlmaLinux · 9 | osbuild-composer-worker | 165.1-4.el9_8.1.alma.1 |
Vulnerabilities 10
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Critical 9.6
Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna
The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For example, ToUnicode("xn--example-.com") incorrectly returns the name "example.com" rather than an error. This behavior can lead to privilege …
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High 7.5
Enforce maximum recursion depth in encoding/asn1
Enforce a recursion limit in Unmarshal to prevent stack exhaustion when parsing deeply-nested, recursive structures.
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High 7.5
Quadratic string concatentation in consumeComment in net/mail
Well-crafted inputs reaching ParseAddress, ParseAddressList, and ParseDate were able to trigger excessive CPU exhaustion and memory allocations.
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High 7.5
Quadratic string concatenation in consumePhrase in net/mail
Pathological inputs could cause DoS through consumePhrase when parsing an email address according to RFC 5322.
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High 7.5
Quadratic complexity in WordDecoder.DecodeHeader in mime
Decoding a maliciously-crafted MIME header containing many invalid encoded-words can consume excessive CPU.
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High 7.5
Apply ReadHeaderTimeout when doing unencrypted HTTP/2 check in net/http
When a server is configured to support unencrypted HTTP/2, it reads a few bytes from each new connection to see if they contain the HTTP/2 client preface. ReadHeaderTimeout is unexpectedly not being applied when doing this.
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High 7.5
Add recursion depth guard during decode in encoding/xml
Previously, DecodeElement would reset the depth counter causing it to never fire; this could lead to stack exhaustion.
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High 7.5
Limit handshake messages we are willing to accept post-handshake in crypto/tls
Handshake messages, such as KeyUpdate, are always considered as state-advancing, regardless of whether a handshake has been completed or not. As a result, a malicious client can keep sending KeyUpdate messages to force the server to keep performing key deriva…
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Medium 6.1
Fix Javascript regexp context tracking in html/template
Previously, pathological inputs could close an unescaped '/' early, allowing for attack-controlled data to inject arbitrary content, potentially leading to XSS.
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Medium 5.9
Avoid quadratic complexity in resolvePath in net/url
Previously, resolving relative paths containing parent directory ('..') segments performed string conversions and buffer rewrites on each step, resulting in quadratic time complexity and high memory allocation overhead. Now, path resolution operates on a byte…
References
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report
https://access.redhat.com/security/cve/CVE-2026-33818
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report
https://access.redhat.com/security/cve/CVE-2026-39820
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report
https://access.redhat.com/security/cve/CVE-2026-39821
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report
https://access.redhat.com/security/cve/CVE-2026-42499
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report
https://access.redhat.com/security/cve/CVE-2026-42504
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report
https://access.redhat.com/security/cve/CVE-2026-56853
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report
https://access.redhat.com/security/cve/CVE-2026-56858
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report
https://access.redhat.com/security/cve/CVE-2026-56859
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report
https://access.redhat.com/security/cve/CVE-2026-56860
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report
https://access.redhat.com/security/cve/CVE-2026-56862
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report
https://bugzilla.redhat.com/2467809
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report
https://bugzilla.redhat.com/2467820
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report
https://bugzilla.redhat.com/2480756
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report
https://bugzilla.redhat.com/2484204
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report
https://bugzilla.redhat.com/2515815
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report
https://bugzilla.redhat.com/2515820
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report
https://bugzilla.redhat.com/2515827
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report
https://bugzilla.redhat.com/2515838
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report
https://bugzilla.redhat.com/2515839
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report
https://bugzilla.redhat.com/2515840
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advisory
https://errata.almalinux.org/9/ALSA-2026-65153.html