vulnerability / NVI-00011936 / Revision 1
Coraza: jsDecode Off-by-One in Octal Escape Handling Enables WAF Bypass
GitHub lists this reviewed advisory for github.com/corazawaf/coraza/v3. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
5.8 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
github.com/corazawaf/coraza/v3
source listed>= 3.0.0, < 3.8.0
### Summary The `t:jsDecode` transformation in Coraza WAF contains an off-by-one error when parsing octal escape sequences. A backslash character was incorrectly included in the octal number buffer, causing `strconv.ParseInt` to fail for every octal escape sequence and return a null byte instead of the decoded value that would normally be returned. This will cause all JS-escaped payloads to be corrupted, thus leading to the bypassing of these WAF rules when WAF rules that rely on `jsDecode` for normalization are enabled. Therefore, a real-world attack scenario: an attacker could use JavaScript octal escape sequences (`\ooo`) to encode attack syntax. Although the WAF cannot decode these sequences correctly, the target backend (such as a browser or application) can parse them as expected. ### Details Vulnerable code: `internal/transformations/js_decode.go:64-70.` ```go case (i+1 < inputLen) && isodigit(input[i+1]): /* \OOO (only one byte, \000 - \377) */ buf := make([]byte, 3) j := 0 for (i+1+j < inputLen) && (j < 3) { buf[j] = input[i+j] // this should be `input[i+1+j]` j++ if !isodigit(input[i+j]) { break } } ``
03 / Response
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- investigate
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04 / Limits
What this report cannot establish
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05 / Provenance
Sources you can inspect
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- GHSA-pc5q-qfxp-ggqv ↗
GitHub Advisory Database · vendor advisory
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- Revision 1 ·
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