diff --git a/api/src/services/text_processing/normalizer.py b/api/src/services/text_processing/normalizer.py
index 13d76763..d84a10ad 100644
--- a/api/src/services/text_processing/normalizer.py
+++ b/api/src/services/text_processing/normalizer.py
@@ -155,11 +155,16 @@
 MONEY_UNITS = {"$": ("dollar", "cent"), "£": ("pound", "pence"), "€": ("euro", "cent")}
 
 # Pre-compiled regex patterns for performance
+# Lengths bounded to RFC limits (64/253) to prevent O(n^2) backtracking on floods.
 EMAIL_PATTERN = re.compile(
-    r"\b[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-z]{2,}\b", re.IGNORECASE
+    r"\b[a-zA-Z0-9._%+-]{1,64}@[a-zA-Z0-9.-]{1,253}\.[a-z]{2,}\b", re.IGNORECASE
 )
 URL_PATTERN = re.compile(
-    r"(https?://|www\.|)+(localhost|[a-zA-Z0-9.-]+(\.(?:"
+    # Token-start lookbehind + 253-char domain bound: without them the domain
+    # branch rescans from every position of a long word run (O(n^2)).
+    r"(?<![a-zA-Z0-9.-])"
+    # Two optionals, not (https?://|www\.|)+ — '+' over an empty alternative is a ReDoS smell.
+    r"(?:https?://)?(?:www\.)?(localhost|[a-zA-Z0-9.-]{1,253}(\.(?:"
     + "|".join(VALID_TLDS)
     + r"))+|[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3})(:[0-9]+)?([/?][^\s]*)?",
     re.IGNORECASE,
@@ -492,7 +497,10 @@ def normalize_text(text: str, normalization_options: NormalizationOptions) -> st
     text = re.sub(r"(?<=[BCDFGHJ-NP-TV-Z])'?s\b", "'S", text)
     text = re.sub(r"(?<=X')S\b", "s", text)
     text = re.sub(
-        r"(?:[A-Za-z]\.){2,} [a-z]", lambda m: m.group().replace(".", "-"), text
+        # {2,12} not {2,} — real acronyms are short; unbounded backtracks O(n^2) on floods.
+        r"(?:[A-Za-z]\.){2,12} [a-z]",
+        lambda m: m.group().replace(".", "-"),
+        text,
     )
     text = re.sub(r"(?i)(?<=[A-Z])\.(?=[A-Z])", "-", text)
 
diff --git a/api/tests/test_normalizer_redos.py b/api/tests/test_normalizer_redos.py
new file mode 100644
index 00000000..32cddae8
--- /dev/null
+++ b/api/tests/test_normalizer_redos.py
@@ -0,0 +1,55 @@
+"""Regression tests for ReDoS / catastrophic-backtracking in the text
+normalizer. Each adversarial input previously drove normalize_text() into
+super-linear time, blocking the async event loop (a single-request DoS,
+since normalize_text runs synchronously inside the request path).
+"""
+
+import time
+
+from api.src.services.text_processing.normalizer import normalize_text
+from api.src.structures.schemas import NormalizationOptions
+
+OPTS = NormalizationOptions()
+BUDGET_S = 2.0  # generous ceiling; pathological inputs previously took 10-65s
+
+
+def _elapsed(payload: str) -> float:
+    start = time.monotonic()
+    normalize_text(payload, OPTS)
+    return time.monotonic() - start
+
+
+def test_long_word_run_is_fast():
+    """URL_PATTERN backtracked from every position of a dotless word run."""
+    assert _elapsed("a" * 100_000) < BUDGET_S
+
+
+def test_dotted_run_is_fast():
+    """'a.a.a...' hit URL/EMAIL domain scans and the dotted-acronym handler."""
+    assert _elapsed("a." * 50_000) < BUDGET_S
+    assert _elapsed(".a" * 50_000) < BUDGET_S
+
+
+def test_at_sign_run_is_fast():
+    """EMAIL_PATTERN local/domain runs on an '@' flood."""
+    assert _elapsed("a@" * 50_000) < BUDGET_S
+
+
+def test_scaling_is_linear():
+    """4x input must cost far less than the ~16x a quadratic scan implies."""
+    small = _elapsed("a." * 25_000)
+    large = _elapsed("a." * 100_000)
+    assert large / max(small, 1e-3) < 9.0
+
+
+def test_url_normalization_preserved():
+    """The hardened patterns must still normalize real URLs and emails."""
+    assert "google" in normalize_text("visit https://google.com now", OPTS)
+    assert "example" in normalize_text("see www.example.com/x", OPTS)
+    out = normalize_text("mail me at a.user@example.org please", OPTS)
+    assert "at" in out and "example" in out
+
+
+def test_dotted_acronym_preserved():
+    """The bounded acronym handler must still hyphenate 'U.S.A. b'."""
+    assert "U-S-A-" in normalize_text("The U.S.A. beats all", OPTS)