diff --git a/ruby4.0.spec b/ruby4.0.spec
index dd02a5a..d6d57c2 100644
--- a/ruby4.0.spec
+++ b/ruby4.0.spec
@@ -356,6 +356,12 @@ Patch13: rubygem-net-imap-0.6.2-ResponseReader-quadratic-complexity-CVE-2026-422
 # - https://github.com/ruby/net-imap/commit/62eea6ff
 # - https://github.com/ruby/net-imap/commit/24d5c773
 Patch14: rubygem-net-imap-0.6.2-STARTTLS-stripping-vulnerability-CVE-2026-42246.patch
+# CVE-2026-42258
+# Fix Net::IMAP command injection vulnerability via unvalidated Symbol arguments
+# Advisory: https://github.com/advisories/GHSA-75xq-5h9v-w6px
+# Sourced from:
+# - https://github.com/ruby/net-imap/commit/9db3e9d
+Patch15: rubygem-net-imap-0.6.2-flag-symbol-validation-CVE-2026-42258.patch
 
 %{?with_rubypick:Suggests: rubypick}
 
@@ -524,6 +530,7 @@ popd
 pushd .bundle/gems/net-imap-%{net_imap_version}
 %patch 13 -p1
 %patch 14 -p1
+%patch 15 -p1
 popd
 
 # Provide an example of usage of the tapset:
@@ -1672,6 +1679,8 @@ make -C %{_vpath_builddir} runruby TESTRUN_SCRIPT=" \
   Resolves: RHEL-181680
 - Fix Net::IMAP STARTTLS stripping vulnerability (CVE-2026-42246)
   Resolves: RHEL-181753
+- Fix Net::IMAP command injection vulnerability via unvalidated Symbol arguments (CVE-2026-42258)
+  Resolves: RHEL-181785
 
 * Wed Apr 29 2026 Tomas Juhasz <tjuhasz@redhat.com> - 4.0.3-34
 - Upgrade to Ruby 4.0.3.
diff --git a/rubygem-net-imap-0.6.2-flag-symbol-validation-CVE-2026-42258.patch b/rubygem-net-imap-0.6.2-flag-symbol-validation-CVE-2026-42258.patch
new file mode 100644
index 0000000..bc61d61
--- /dev/null
+++ b/rubygem-net-imap-0.6.2-flag-symbol-validation-CVE-2026-42258.patch
@@ -0,0 +1,98 @@
+From 9db3e9d Mon Sep 17 00:00:00 2001
+From: nick evans <nick@rubinick.dev>
+Date: Thu, 19 Feb 2026 15:06:08 -0500
+Subject: [PATCH] =?UTF-8?q?=F0=9F=A5=85=20Strictly=20validate=20symbol=20(?=
+ =?UTF-8?q?\flag)=20arguments?=
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+Flags should not allow `atom-specials`.
+
+Previously, no validation was done on symbol data.  Sending atom or flag
+args which contain atom specials could lead to various errors.
+
+Although this could theoretically include injection attacks, this is not
+considered to be a critical vulnerability in `net-imap`, for the
+following reason:  Valid "system flag" inputs are restricted to an
+enumerated set of RFC-defined flag types.  User-defined "keyword" flags
+are sent as atoms, not flags, which use string inputs (strings which
+can't be sent as an atom will be quoted or sent as a literal).  `\Seen`
+as a flag (symbol argument) is semantically different from `Seen` as a
+keyword (string argument).  So there is no scenario where it is
+appropriate to call `#to_sym` on unvetted user input.  Any code which
+calls `#to_sym` indiscriminately on user-input is already buggy.
+
+Nevertheless, users should reasonably be able to rely on `net-imap` to
+do very basic input validation on its basic input types.
+---
+ lib/net/imap/command_data.rb | 33 +++++++++++++++++++++++++++------
+ 1 file changed, 27 insertions(+), 6 deletions(-)
+
+diff --git a/lib/net/imap/command_data.rb b/lib/net/imap/command_data.rb
+index 02b9a61..2671d5d 100644
+--- a/lib/net/imap/command_data.rb
++++ b/lib/net/imap/command_data.rb
+@@ -25,6 +25,7 @@ module Net
+         end
+       when Time, Date, DateTime
+       when Symbol
++        Flag.validate(data)
+       else
+         data.validate
+       end
+@@ -45,7 +46,7 @@ module Net
+       when Date
+         send_date_data(data)
+       when Symbol
+-        send_symbol_data(data)
++        Flag[data].send_data(self, tag)
+       else
+         data.send_data(self, tag)
+       end
+@@ -115,11 +116,13 @@ module Net
+     def send_date_data(date) put_string Net::IMAP.encode_date(date) end
+     def send_time_data(time) put_string Net::IMAP.encode_time(time) end
+ 
+-    def send_symbol_data(symbol)
+-      put_string("\\" + symbol.to_s)
+-    end
+-
+     CommandData = Data.define(:data) do # :nodoc:
++      def self.validate(...)
++        data = new(...)
++        data.validate
++        data
++      end
++
+       def send_data(imap, tag)
+         raise NoMethodError, "#{self.class} must implement #{__method__}"
+       end
+@@ -135,8 +138,26 @@ module Net
+     end
+ 
+     class Atom < CommandData # :nodoc:
++      def initialize(**)
++        super
++        validate
++      end
++
++      def validate
++        data.to_s.ascii_only? \
++          or raise DataFormatError, "#{self.class} must be ASCII only"
++        data.match?(ResponseParser::Patterns::ATOM_SPECIALS) \
++          and raise DataFormatError, "#{self.class} must not contain atom-specials"
++      end
++
+       def send_data(imap, tag)
+-        imap.__send__(:put_string, data)
++        imap.__send__(:put_string, data.to_s)
++      end
++    end
++
++    class Flag < Atom # :nodoc:
++      def send_data(imap, tag)
++        imap.__send__(:put_string, "\\#{data}")
+       end
+     end
+