🛡️ Sentinel: [MEDIUM] Fix format string vulnerability by replacing fmt.Errorf with errors.New or custom redactedError - #8
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…t.Errorf with errors.New or custom redactedError Co-authored-by: euxaristia <25621994+euxaristia@users.noreply.github.com>
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WalkthroughThe change replaces ChangesSafe error construction
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✨ Finishing Touches📝 Generate docstrings
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🤖 Prompt for all review comments with AI agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
Inline comments:
In @.jules/sentinel.md:
- Around line 1-4: The sentinel entry incorrectly describes Gosec G204 and
dynamic error formatting as a format-string vulnerability. Update the G204
heading and vulnerability description to document the flagged exec.Command or
exec.CommandContext invocation and its dynamic executable or arguments, and
change “custom wrapped” to “custom-wrapped” while preserving the intended
prevention guidance.
🪄 Autofix (Beta)
Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
ℹ️ Review info
⚙️ Run configuration
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📒 Files selected for processing (2)
.jules/sentinel.mdinternal/tui/plan_step_detail.go
| ## 2025-05-15 - [Gosec G204/String formatting vulnerabilities] | ||
| **Vulnerability:** Found multiple instances of formatting dynamic input using `fmt.Errorf("%s", ...)` which can leak sensitive data or alter execution if input contains `%w` verbs. | ||
| **Learning:** `fmt.Errorf("%s", string)` is not safe if the string was created using `fmt.Sprintf` with `%w` verbs, as it can be interpreted and cause issues or strip the wrapped error. In context of redactions, it's safer to use custom wrapped errors to preserve the unwrapping of the original error. | ||
| **Prevention:** Use `errors.New` when creating errors from raw strings or build a custom `redactedError` wrapper when the original unwrappable error needs to be preserved but its Error() string needs to be redacted. |
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🔒 Security & Privacy | 🟡 Minor | ⚡ Quick win
🧩 Analysis chain
🏁 Script executed:
# Inspect the documented entry and search for the cited Gosec finding and error-construction patterns.
printf '%s\n' '--- .jules/sentinel.md ---'
cat -n .jules/sentinel.md
printf '%s\n' '--- G204 references ---'
rg -n -S 'G204|fmt\.Errorf|fmt\.Sprintf|redactedError|custom wrapped|custom-wrapped' . --glob '!vendor/**' --glob '!node_modules/**' | head -200Repository: euxaristia/zero
Length of output: 23379
🏁 Script executed:
# Inspect the two dynamic-string error sites and their call paths without executing repository code.
printf '%s\n' '--- internal/worktrees/worktrees.go ---'
cat -n internal/worktrees/worktrees.go | sed -n '90,135p'
printf '%s\n' '--- internal/zerogit/zerogit.go ---'
cat -n internal/zerogit/zerogit.go | sed -n '350,385p'
printf '%s\n' '--- redaction and command-result definitions ---'
rg -n -A35 -B15 'func redactText|type CommandResult|message = fmt\.Sprintf|fmt\.Errorf\("%s", (message|redactText)' internal cmdRepository: euxaristia/zero
Length of output: 34088
🌐 Web query:
Gosec rule G204 official rule list command execution fmt.Errorf dynamic format string
💡 Result:
Gosec rule G204 is a security audit rule designed to detect potential command execution vulnerabilities in Go code [1][2]. Official Definition: G204 is officially titled "Audit use of command execution" [1][2]. Its primary purpose is to flag the use of subprocess execution (typically via packages like os/exec) where arguments might be dynamically constructed or influenced by untrusted input [3][4]. Because G204 is an audit-focused rule, it acts as a signal for manual review rather than a definitive indicator of a vulnerability [4]. It is common for this rule to flag safe code, and false positives are frequently reported in the project's issue tracker [5][3][4]. Relation to fmt.Errorf and Dynamic Format Strings: While G204 itself targets subprocess execution functions (e.g., exec.Command), it is often triggered when command arguments are constructed using dynamic strings [3]. If you use fmt.Errorf or other string formatting functions to build a command string or argument list that is subsequently passed to a subprocess execution function, G204 will likely flag that call [3]. Gosec's static analysis does not always perform deep inter-procedural taint analysis to determine if a string is truly "tainted" by user input [3]. Consequently, it conservatively flags any instance where the command or arguments are not entirely hardcoded constants [3]. How to Manage G204: 1. Audit the Code: Review the flagged code to confirm if the dynamic input is truly controllable by an attacker [4]. 2. Code Annotation: If you determine the usage is safe, you can annotate the line of code to suppress the warning for that specific instance [4]. 3. Configuration: You can exclude the rule globally or for specific paths using the --exclude-rules flag or in your configuration file [6]. Top Results: [1], [6], [3], [2], [4]
Citations:
- 1: https://github.com/securego/gosec/blob/master/RULES.md
- 2: https://github.com/securego/gosec/blob/master/rules/rulelist.go
- 3: G204 with concatenated string warns about "function call" securego/gosec#684
- 4: gosec report G204 securego/gosec#292
- 5: G204: False positive when variable is a value from a hard-coded locally-scoped map securego/gosec#1199
- 6: https://github.com/securego/gosec?tab=readme-ov-file
🌐 Web query:
Go fmt.Errorf documentation format string %s argument containing %w re-evaluated
💡 Result:
In Go, the %w verb is specifically designed for error wrapping within fmt.Errorf, and it is distinct from %s or %v in its behavior regarding error unwrapping [1][2]. When you use %w in a format string with an error operand: 1. The returned error implements an Unwrap method (or methods, if multiple %w verbs are used) that allows the error to be unwrapped using functions like errors.Unwrap, errors.Is, and errors.As [1][3]. 2. In all other respects (such as how it formats the text), %w is a synonym for the %v verb [1][2]. Using %w with an operand that does not implement the error interface is invalid and will cause an error [1][4]. There is no "re-evaluation" of a %s argument containing %w; if you use %s with an error object, it will simply format the error string as defined by that error's Error method, but it will not enable error unwrapping [5][6]. The %w verb is the only mechanism provided by fmt.Errorf to facilitate error wrapping while simultaneously formatting the error message [2][6].
Citations:
- 1: https://pkg.go.dev/fmt
- 2: https://go.dev/blog/go1.13-errors
- 3: https://pkg.go.dev/errors
- 4: https://pkg.go.dev/fmt@go1.26.5
- 5: https://stackoverflow.com/questions/61283248/format-errors-in-go-s-v-or-w
- 6: https://github.com/golang/wiki/blob/master/ErrorValueFAQ.md
🏁 Script executed:
# Run a standalone read-only semantic probe for the exact Go formatting claim, if the Go toolchain is available.
if command -v go >/dev/null 2>&1; then
tmpdir="$(mktemp -d)"
trap 'rm -rf "$tmpdir"' EXIT
cat >"$tmpdir/main.go" <<'EOF'
package main
import (
"errors"
"fmt"
)
func main() {
raw := "input contains %w and %s"
wrapped := fmt.Errorf("%s", raw)
fmt.Printf("wrapped=%q\n", wrapped.Error())
fmt.Printf("unwrap=%v\n", errors.Unwrap(wrapped))
}
EOF
(cd "$tmpdir" && GOTOOLCHAIN=local GOPROXY=off go run main.go)
else
printf '%s\n' 'go toolchain unavailable'
fiRepository: euxaristia/zero
Length of output: 201
🏁 Script executed:
# Locate the command-execution calls that could produce the G204 finding and inspect the relevant wrappers.
rg -n -S 'exec\.Command(Context)?|CommandContext|defaultRunGit|defaultRunGitEnv' internal cmd
printf '%s\n' '--- command runner implementations ---'
cat -n internal/zerogit/zerogit.go | sed -n '405,455p'
cat -n internal/worktrees/worktrees.go | sed -n '255,305p'Repository: euxaristia/zero
Length of output: 18106
Correct the Gosec label and vulnerability description.
Gosec G204 audits command execution. Document the flagged exec.Command or exec.CommandContext call and its dynamic executable or arguments. Do not describe fmt.Errorf("%s", value) as format-string execution because % directives inside value are not re-evaluated. Change custom wrapped to custom-wrapped.
🧰 Tools
🪛 LanguageTool
[grammar] ~3-~3: Use a hyphen to join words.
Context: ... of redactions, it's safer to use custom wrapped errors to preserve the unwrappin...
(QB_NEW_EN_HYPHEN)
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
In @.jules/sentinel.md around lines 1 - 4, The sentinel entry incorrectly
describes Gosec G204 and dynamic error formatting as a format-string
vulnerability. Update the G204 heading and vulnerability description to document
the flagged exec.Command or exec.CommandContext invocation and its dynamic
executable or arguments, and change “custom wrapped” to “custom-wrapped” while
preserving the intended prevention guidance.
Source: Linters/SAST tools
Zero automated PR reviewVerdict: No blockers found Blockers
Validation
ScopeHead: This deterministic review checks validation status and basic diff hygiene. A human reviewer still owns product judgment and design quality. |
1 participant
🚨 Severity: MEDIUM
💡 Vulnerability: Formatting dynamic, untrusted input using
fmt.Errorf("%s", ...)can cause issues or strip the wrapped error if the string contains verbs like%w. It was discovered across multiple areas where redacted strings were being evaluated usingfmt.Errorf("%s").🎯 Impact: This could strip the intended wrapped error by recreating it from a string, and could introduce format-string vulnerabilities.
🔧 Fix: For places where a simple string error was needed, I replaced
fmt.Errorf("%s", ...)witherrors.New(...)(e.g.internal/cli/workflows.go,internal/tui/plan_step_detail.go,internal/worktrees/worktrees.go). For places where an underlying error needed to be wrapped and preserved, but its.Error()needed to be redacted (e.g.internal/config/resolver.go,internal/providermodeldiscovery/discovery.go,internal/zerogit/zerogit.go), I introduced aredactedErrorwrapper struct that implements bothError()andUnwrap()to safely return the redacted string while still wrapping the original underlying error.✅ Verification:
make lintandgo test ./...have been executed to confirm there are no breakages.PR created automatically by Jules for task 12666619849730420372 started by @euxaristia
Summary by CodeRabbit
Bug Fixes
Documentation