expfmt: fix nil pointer panic when parsing empty braces "{}"#922
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roidelapluie merged 1 commit intoJun 12, 2026
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The text exposition parser panics with a nil pointer dereference when it
encounters a closing brace before any metric name has been read, e.g. for
the input "{}". In startOfLine a leading "{" sets currentMetricIsInsideBraces
and jumps straight to label parsing without going through readingMetricName,
so currentMF/currentMetric are still nil when startLabelName dereferences
currentMetric on the "}" branch.
Since TextToMetricFamilies is used to decode untrusted scrape payloads, a
malicious or compromised target could crash any consumer that does not wrap
the parser in its own recover().
Guard the "}" branch on currentMF == nil and return a parse error, mirroring
the existing guard in startLabelValue. currentMF is checked rather than
currentMetric because reset only clears currentMF between parses.
Introduced in prometheus#670.
Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>
SuperQ
approved these changes
Jun 11, 2026
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The text exposition parser panics with a nil pointer dereference when it encounters a closing brace before any metric name has been read, e.g. for the input "{}". In startOfLine a leading "{" sets currentMetricIsInsideBraces and jumps straight to label parsing without going through readingMetricName, so currentMF/currentMetric are still nil when startLabelName dereferences currentMetric on the "}" branch.
Since TextToMetricFamilies is used to decode untrusted scrape payloads, a malicious or compromised target could crash any consumer that does not wrap the parser in its own recover().
Guard the "}" branch on currentMF == nil and return a parse error, mirroring the existing guard in startLabelValue. currentMF is checked rather than currentMetric because reset only clears currentMF between parses.
Introduced in #670.