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security/89: Add patch which can optionally be used to work around CVE-2021-45444 in VCS_Info
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Marc Cornellà
dana
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2 changed files with 103 additions and 0 deletions
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2022-01-27 dana <dana@dana.is>
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* Marc Cornellà: security/89:
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Etc/CVE-2021-45444-VCS_Info-workaround.patch: Add patch which
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can optionally be used to work around recursive PROMPT_SUBST
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issue in VCS_Info
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* Oliver Kiddle: security/41: Src/prompt.c: Prevent recursive
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PROMPT_SUBST
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98
Etc/CVE-2021-45444-VCS_Info-workaround.patch
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98
Etc/CVE-2021-45444-VCS_Info-workaround.patch
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From 972887bbe5eb6a00e5f0e73781d6d73bfdcafb93 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Marc=20Cornell=C3=A0?= <hello@mcornella.com>
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Date: Mon, 24 Jan 2022 09:43:28 +0100
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Subject: [PATCH] security/89: Partially work around CVE-2021-45444 in VCS_Info
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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This patch is a partial, VCS_Info-specific work-around for CVE-2021-45444,
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which is mitigated in the shell itself in 5.8.1 and later versions. It is
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offered for users who are concerned about an exploit but are unable to update
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their binaries to receive the complete fix.
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The patch works around the vulnerability by pre-escaping values substituted
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into format strings in VCS_Info. Please note that this may break some user
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configurations that rely on those values being un-escaped (which is why it was
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not included directly in 5.8.1). It may be possible to limit this breakage by
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adjusting exactly which ones are pre-escaped, but of course this may leave
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them vulnerable again.
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If applying the patch to the file system is inconvenient or not possible, the
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following script can be used to idempotently patch the relevant function
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running in memory (and thus must be re-run when the shell is restarted):
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# Impacted versions go from v5.0.3 to v5.8 (v5.8.1 is the first patched version)
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autoload -Uz is-at-least
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if is-at-least 5.8.1 || ! is-at-least 5.0.3; then
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return
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fi
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# Quote necessary $hook_com[<field>] items just before they are used
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# in the line "VCS_INFO_hook 'post-backend'" of the VCS_INFO_formats
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# function, where <field> is:
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#
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# base: the full path of the repository's root directory.
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# base-name: the name of the repository's root directory.
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# branch: the name of the currently checked out branch.
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# revision: an identifier of the currently checked out revision.
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# subdir: the path of the current directory relative to the
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# repository's root directory.
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# misc: a string that may contain anything the vcs_info backend wants.
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#
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# This patch %-quotes these fields previous to their use in vcs_info hooks and
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# the zformat call and, eventually, when they get expanded in the prompt.
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# It's important to quote these here, and not later after hooks have modified the
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# fields, because then we could be quoting % characters from valid prompt sequences,
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# like %F{color}, %B, etc.
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#
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# 32 │ hook_com[subdir]="$(VCS_INFO_reposub ${hook_com[base]})"
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# 33 │ hook_com[subdir_orig]="${hook_com[subdir]}"
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# 34 │
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# 35 + │ for tmp in base base-name branch misc revision subdir; do
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# 36 + │ hook_com[$tmp]="${hook_com[$tmp]//\%/%%}"
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# 37 + │ done
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# 38 + │
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# 39 │ VCS_INFO_hook 'post-backend'
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#
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# This is especially important so that no command substitution is performed
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# due to malicious input as a consequence of CVE-2021-45444, which affects
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# zsh versions from 5.0.3 to 5.8.
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#
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autoload -Uz +X regexp-replace VCS_INFO_formats
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# We use $tmp here because it's already a local variable in VCS_INFO_formats
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typeset PATCH='for tmp (base base-name branch misc revision subdir) hook_com[$tmp]="${hook_com[$tmp]//\%/%%}"'
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# Unique string to avoid reapplying the patch if this code gets called twice
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typeset PATCH_ID=vcs_info-patch-9b9840f2-91e5-4471-af84-9e9a0dc68c1b
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# Only patch the VCS_INFO_formats function if not already patched
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if [[ "$functions[VCS_INFO_formats]" != *$PATCH_ID* ]]; then
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regexp-replace 'functions[VCS_INFO_formats]' \
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"VCS_INFO_hook 'post-backend'" \
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': ${PATCH_ID}; ${PATCH}; ${MATCH}'
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fi
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unset PATCH PATCH_ID
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---
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Functions/VCS_Info/VCS_INFO_formats | 4 ++++
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1 file changed, 4 insertions(+)
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diff --git a/Functions/VCS_Info/VCS_INFO_formats b/Functions/VCS_Info/VCS_INFO_formats
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index e0e1dc738..4d88e28b6 100644
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--- a/Functions/VCS_Info/VCS_INFO_formats
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+++ b/Functions/VCS_Info/VCS_INFO_formats
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@@ -32,6 +32,10 @@ hook_com[base-name_orig]="${hook_com[base_name]}"
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hook_com[subdir]="$(VCS_INFO_reposub ${hook_com[base]})"
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hook_com[subdir_orig]="${hook_com[subdir]}"
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+for tmp in base base-name branch misc revision subdir; do
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+ hook_com[$tmp]="${hook_com[$tmp]//\%/%%}"
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+done
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+
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VCS_INFO_hook 'post-backend'
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## description (for backend authors):
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--
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2.34.1
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